Barcelona all but won the Champions League semifinal when Pedro netted in the 53rd minute.
The second leg match was all tied up but Iniesta produced a class ball and Pedro slotted it past Casillas who had a great game up to that stage.
But then just 10 minutes later Real Madrid got one back and tied it up again.
Di Maria beat one at the edge of the box and then knocked a shot off the post. It rebounded back to him and he has the presence of mind to lay it square for Marcelo, who slammed it into the net
The match finished 1-1 with Barcelona going through to the Wembley final 3-1 on aggregate to either face Manchester United or Schalke.
Teams:
Barcelona: Víctor Valdés, Dani Alves, Carles Puyol, Gerard Piqué, Javier Mascherano, Sergio Busquets, Xavi, Andrés Iniesta, Pedro, Lionel Messi, David Villa.
Real Madrid: Iker Casillas, Marcelo, Álvaro Arbeloa, Ricardo Carvalho, Raúl Albiol, Ángel Di María, Lass Diarra, Xabi Alonso, Kaká, Cristiano Ronaldo, Gonzalo Higuaín.
Pre-game
The second leg of the Champions League semi-final between Barcelona and Real Madrid takes place at the Nou Camp with the Catalan side carrying a healthy 2-0 advantage to their home base after last week's acrimonious encounter at the Bernabeu.
On the eve of the match, Pep Guardiola's men put the final touches to their preparations for a possible seventh appearance in the final of European club football's premier competition, but the pre-match talk spent little time on the football itself.
Midfielder Xavi Hernandez and his coach Pep Guardiola had to field question after question about possible sanctions on both sides after accusations of institutional bias in favour of Barcelona from Real Madrid and that 'Barca' - often cited as the most attractive side in world football - have a darker side to their game in terms of play acting and what UEFA term as 'simulation'.
It’s a serene-looking Barcelona side prepared for their latest encounter with arch-rivals Real Madrid, eyeing a fourth appearance in the final of the UEFA Champions League and a seventh European championship final overall.
Last week in Madrid, two goals from the Catalan club's mercurial Argentine striker, Lionel Messi, gave 'Barca' a 2-0 victory and a huge advantage going into the second leg.
However, his efforts were overshadowed by two red cards in the game, a half-time brawl, and Real coach Jose Mourinho crying 'foul' over alleged bias towards 'Pep' Guardiola's side.
'Barca' midfielder Xavi Hernandez attempted to put Tuesday night's game back into its 'proper' perspective.
"For us it is a pleasure to be here playing semi-final stages of Champions (League) and to be able to enjoy this. We have a very good first leg result. We want our supporters to have a good time and enjoy the moment. This is a historic moment with a historical rival such as Real Madrid in front of us. We think it is fantastic to be able to reach this stage in these conditions,” says Hernandez.
Xavi had little success in steering the pre-match discussions away from off-field matters and even fell into the trap of talking about Real coach Jose Mourinho - a double Champions League winner with Porto and Inter Milan.
Mourinho will be serving a touchline ban on Tuesday night for protesting too vehemently against the sending off of his Portuguese defender Pepe in the 61st minute of the first leg - Messi scored both Barca's goals after that contentious incident.
"It is sad for me to be asked to talk about things that are not related to sport. Things that have nothing to do with this great sport called football. We always try to do our best on the pitch, always with great respect towards our rivals and play our game. Evidently (Real) Madrid have their weapons such as their coach. He (Jose Mourinho) is a coach who likes the polemics, not only because of the latest events but since forever. But we try to remain outside of these games."
Mourinho faces further charges from UEFA for suggesting that there is a pro-Barcelona bias within the game, but the allegation clearly stung Xavi, who protested that Barcelona always try to play football in the right spirit and with an open style.
"This type of denunciation doesn't lead anywhere. UEFA has obviously disregarded these accusations and that's it. We try to talk about our football and not about these lamentable details."
Barca coach Pep Guardiola had better luck in keeping the comment centred on matters pertaining to the pitch.
Guardiola warned his own players - and Barca fans - against complacency, as their opponents will have little to lose.
"We have talked about the fact that tomorrow that we need to be prepared for anything. All of them (Real Madrid) know how to play football very well. They are capable of putting pressure on us in our penalty area as well as being able to attack us in the midfield and in their area. All that will dictate how they will attack and defend. We have to be prepared. Tomorrow is like a final. And in a final game you don't speculate because there will be a second leg. And that will be all. The only reality is that tomorrow Real Madrid will play the game of their life in order to make it to the final. That is the only fact we know.,” says Guardiola.
After four matches against the 'Old Enemy' already this season - Barca have won two, drawn one and lost the Copa del Rey final 1-0 last week - Guardiola says he will be happy to finally complete a fifth 'Clasico' tomorrow night.
"We are lucky that tomorrow finishes. We are lucky. Tomorrow finishes everything. So tomorrow we have a game at 20:45 (PM, Local Time. 19:45 GMT) and after that we are going to finish everything. So we are lucky."
With a two-nil advantage and the home leg to come, many pundits are already assuming that Barcelona will take their place in the Champions League final against either Manchester United of England or Germany's Schalke 04.
Guardiola was not taking anything for granted, but said that it would be fantastic for Barca to reach another milestone in their history and perhaps even win a fourth European crown.
"We play to reach a final in as much that Real Madrid will play to reach a final. The draw told us we had to face Real Madrid, but it could have been any other team. We won't play to eliminate Real Madrid. We'll play to reach the final stage of Champions League. One year it is Inter (Milan), another Chelsea and in future years I wish we could be able to face many more teams. We play ninety minutes so we can defeat our opponent and reach the final game."
Barca already have one hand on the Spanish league title and they will be hot favourites to make it through to a seventh European championship final.
Only twice in the Champions League have teams overturned first-leg defeats at home in the knockout stages - outgoing holders Inter Milan did so earlier this season against Bayern Munich and Dutch side Ajax came back to beat Panathinaikos in 1996.
Add to that the fact that 'Barca' also have Messi in their line-up and Real Madrid's task becomes mountainous indeed.
Meanwhile, UEFA is sending Italian refereeing great Pierluigi Collina to monitor Belgian match official Frank de Bleeckere's handling of a potentially volatile Champions League semifinals clash between Barcelona and Real Madrid.
UEFA has named Collina, its head of referees, as its official observer at the Camp Nou.
While UEFA sends a referee observer to every match it organises, it is rare for Collina to be called in.
UEFA's choice of the 44-year-old de Bleeckere, who has a long-standing reputation as one of Europe's best referees, also reflects the high-risk status it has given the rematch of storied Spanish rivals.
After Barcelona won a bad-tempered first leg 2-0 last Wednesday, Madrid made a failed protest to UEFA about German referee Wolfgang Stark sending off Pepe when the game was scoreless.
Madrid coach Jose Mourinho was sent from the dugout by Stark for his comments about Pepe's red card, then later accused UEFA and its referees of actively helping Barcelona reach Champions League finals.
Mourinho included de Bleeckere in the supposed conspiracy after his handling of the second leg of last year's semifinal when the Portuguese coach's 10-man Inter Milan side eliminated Barcelona.
UEFA named another Italian official, Sergio di Cesare, to serve as its match delegate on Tuesday.
UEFA's disciplinary panel will meet Friday to examine six charges arising from the first-leg match.
Mourinho, who is banned from the touchline Tuesday, faces further punishment for his comments during and after the match. Pepe also faces a longer ban for his red-card challenge, and Madrid has been charged for its fans throwing objects and invading the pitch.
Barcelona's substitute goalkeeper Jose Pinto has been charged over his part in a touchline brawl at halftime.
Collina was referee for the second leg when Madrid and Barcelona last met in the Champions League semifinals.
In 2002, the sides drew 1-1 at the Santiago Bernabeu stadium allowing Madrid to advance and win the title.
Collina also refereed the 2002 World Cup final, when Brazil beat Germany 2-0, and Manchester United's 2-1 victory over Bayern Munich in the 1999 Champions League final.
Pre-game controversy
Pep Guardiola's side took a 2-0 win away from the Santiago Bernabeu on Thursday in a game marred by red cards to Real Madrid defender Pepe and manager Jose Mourinho, as well as Barcelona reserve goal-keeper Jose Pinto.
Real Madrid appealed against the red card handed to Pepe for his challenge on Dani Alves, and also accused Barcelona's players of provoking the defender throughout the match.
But yesterday the governing body dismissed the protests, meaning Pepe will be banned for the return leg at the Nou Camp on Wednesday.
"In the case of the behaviour of the FC Barcelona players, it was deemed that there was no common strategy to provoke the Real Madrid CF player, while in the case of Pepe, the referee's factual decision is upheld," a UEFA statement read.
Barcelona lodged a complaint against Mourinho for his post-game comments, in which the Portuguese manager claimed there was a conspiracy against his side.
"No one has any chance against Barca. Where does all this power come from? To win like this is very nasty," Mourinho said after the match.
"Why do the opponents of Barcelona always have a man sent off? Where does this power come from? Maybe it is to give more publicity to UNICEF, maybe because of the power of (Spanish federation president Jose Angel) Villar in UEFA."
But UEFA dismissed Barcelona's complaint because Mourinho is already set to face the Control and Disciplinary Body on Friday to explain his comments."
In this instant, FC Barcelona have been referred to the proceedings already brought against Jose Mourinho," the statement said.
Both clubs have three days to appeal the decisions.
Leg 1 wrap
Lionel Messi lit up an ill-tempered Champions League semifinal (Leg 1) with two goals in the last 15 minutes to give Barcelona a 2-0 victory at 10-man Real Madrid in El Clásico 3 – the third time in a short few weeks that the two teams have met.
Messi guided substitute Ibrahim Afellay's cross through the legs of goalkeeper Iker Casillas to open the scoring in the 76th minute.
Click for tempers flaring at halftime
See extended coverage of both Lionel Messi's goals
With three minutes to play, the elusive Argentina forward brilliantly ghosted past three defenders before clipping the ball past Madrid goalkeeper Iker Casillas for his 52nd goal of the season, and 11th in the Champions League.
Barcelona dominated throughout but only managed to break through after Pepe was red-carded in the 61st at the Santiago Bernabeu Stadium.
Madrid coach Jose Mourinho was sent to the stands for protesting the decision, which left Madrid playing with 10 against Barcelona for the fourth straight game.
Mourinho has seen his team finish with 10 players in his last five matches against Barcelona, counting Inter Milan's 1-0 defeat at Barcelona in the semifinal return leg last year.
"If I say to (the referee) and to UEFA what I think and feel, my career ends today," Mourinho said. "One day I hope to get an answer to the question: why?"
It was Barcelona's first win in three games between the bitter rivals in 12 days after a 1-1 league draw and a 1-0 extra-time Copa del Rey final defeat.
Madrid's defense in Tuesday's return leg will be short-handed with Pepe and Sergio Ramos both suspended. Ramos was booked for a foul on Messi in the 53rd.
Mourinho described the second leg in Barcelona as "mission impossible" as he continued to bemoan his side's treatment by the referee.
"We'll go there with pride, without Pepe who did nothing, without Ramos who did nothing and the coach who can't be on the bench," he said. "If we score a goal they'll kill us again. It's a result that is impossible.
"Today showed we have no possibility. And my question is why? I'll live my whole life with this question but I hope one day to get the answer. Why in a game that was equal did he do what he did? But he won't answer, he'll go home because he doesn't have to answer to anyone."
Counterpart Pep Guardiola refused to respond to Mourinho's comments, preferring to congratulate his team's performance.
"A team that has nine European Cups never gives up on a series, I'm convinced of that," Guardiola said. "We played a very good game. We controlled their counterattacks, their aerial game which is very dangerous."
Messi's 178th goal tied him with Josep Samitier as the third highest scorer for Barcelona, behind only Cesar Rodriguez (235) and Laszlo Kubala (196).
"At 23 he's the third leading scorer in club history. That's incredible," Guardiola said.
Both coaches had stoked tensions on the eve of the match, with Guardiola launching an expletive-filled attack on Mounrinho, and the ill-will spilled over into the match.
Substitute Barcelona 'keeper Jose Manuel Pinto was the first to be sent off for a red card at halftime as the two teams skirmished while leaving the field.
Pinto's sending off left Barcelona without a reserve 'keeper as the frustration of being unable to exploit 70 percent of the possession in the first 45 minutes seemed to boiled over.
Pepe was then harshly sent off after clashing with Daniel Alves as he lunged for a ball and Mourinho was sent to the stands for sarcastically clapping and showing a thumbs up to the fourth official.
"If you know football you know that's not a yellow card," said Madrid winger Cristiano Ronaldo, who was limited to testing Barcelona 'keeper Victor Valdes with a dipping shot before the half and a header over the bar after the restart. "The coach was set to make changes over the last 20 minutes."
Barcelona dominated possession as expected from the start and Madrid defended while looking for an opportunity to counterattack, which only materialised when Emmanuel Adebayor came on at the start of the second half.
The visitors patiently threaded the ball around and David Villa and Xavi Hernandez nearly put the Catalans ahead with good chances as Madrid clamped down the center with Pepe sticking to Xavi and Messi.
Tensions finally exploded in the 40th when Madrid defender Alvaro Arbeloa was booked after a tussle with Pedro Rodriguez, while Alves was shown a yellow card for a push on Di Maria.
As the second-half minutes ticked down, Madrid looked set to succeed in frustrating Barca, but Pepe's expulsion complicated things.
Mourinho took a seat in the first row behind the dugout and began scribbling instructions that were passed to assistant coach Aitor Karanka, as he looked to reshuffle his team in the absence of his defensive lynchpin.
But there was no stopping Messi, whose second goal was a wonderful example of his trademark darting run and finish.
Madrid stumbled against Barcelona again at the Bernabeu, where it hasn't beaten Barcleona in nearly three years - a run of four games.
"The expulsion marred the game," Casillas said. "We'll have to see now if anything happens in the return game, which is very complicated from the result."
Apart from hitting out at the officiating, Mourinho also continued his war of words with Guardiola by insisting that if the Catalans coach wins his second Champions League title it will be marred by Wednesday's result.
"I've won two Champions Leagues and I won them both on the field and they were with two clubs," the Portuguese coach said. "Josep Guardiola is a fantastic coach, I repeat he is a fantastic coach. But if he wins again then it will be affected by today."
