Last Updated: 03/04/12 10:38pm
And it's all over at Camp Nou! Barcelona are in the semi-finals for the fifth successive season, courtesy of two penalties from Lionel Messi. Thanks for joining us tonight, stay tuned for a full match report and all the best reaction.
Valdes has to be alert to come off his line with Robinho lurking and although he does not gather cleanly, Barcelona clear the danger.
Messi is close to his third as Alves' cross is pawed away by Abbiati at full stretch, before Nesta completes the clearance.
Messi sets off on one of his jinking, weaving runs through the Milan defence, but is eventually crowded out.
Pato, who has been on the field all of 13 minutes, heads back to the bench with yet another injury problem and Maxi Lopez comes on.
A long ball out of defence almost picks out Pato, but his first touch does not bring the ball under control and Valdes races out to gather.
Important header from Dani Alves to flick the ball away from Aquilani after Ibrahimovic's dangerous cross.
Great chance for Barca! Superb control from Messi as he takes the ball outside the area before laying it into the path of Thiago, but the substitute can only fire across goal and wide of the target.
Dani Alves powers towards the Milan area, with the defence backing off. He attempts to find Messi, but Antonini slides in with an important challenge to divert the ball back to Abbiati.
Thiago attempts to release Fabregas as he bursts into the area, but the ball strikes the heels of the former Arsenal man.
Barca make a change with Xavi, who was an injury doubt prior to the game, heading off to be replaced by Thiago Alcantara.
Great save from Valdes as Robinho charges down Pique's attempted clearance for bursting through, but the whistle had already gone for a very harsh handball decision against the Brazilian.
Shocking marking from Barcelona, as Boateng is in acres of space but can only flick the corner over the bar.
Milan have it all to do now. They're more than capable of breaching Barca's defence, but whether they can keep the home side out is another matter, particularly as they will have to chase the game.
Barcelona now have one foot in the semi-finals, with Messi's shot blocked by Mexes on the edge of the box and looping up and into the path of Andres Iniesta, who shows great composure to control and then beat Abbiati from close range.
Boateng earns Milan a corner, which Seedorf takes short. When the ball is flighted into the box, Valdes punches clear well under pressure but the flag is up.
More possession football from Barca as they probe for an opening. Milan are currently standing firm.
Abbiati is scrambling across his line as Xavi's powerful curling effort from 25 yards out flies narrowly wide of the top corner.
Seedorf flights a ball into the area towards Ibrahimovic, who goes to ground after a challenge from Mascherano, but the referee is not interested.
Kuipers brings an enthralling half to a close. Messi's two penalties have Barca in the lead, but a draw will be enough to take Milan through.
Messi goes close again, but Abbiati manages it to scramble away, with the ball flying goalwards after a quick pass in to the Barca ace.
Milan shoot themselves in the foot as Nesta hauls down Busquets at the corner, with ref Kuipers pointing to the spot. Nesta and Seedorf are booked in the aftermath, with Messi sending Abbiati the wrong way as he finds the opposite bottom corner.
Fabregas is the next to try his luck from range, but his low shot is easy enough for Abbiati to gather.
Messi whips a dangerous free-kick into the Milan penalty area, but there is just too much pace on the ball and it goes beyond Fabregas.
Brilliant play from Fabregas to set up Xavi on the edge of the area and his powerful effort is parried away by Abbiati.
Great play from Milan to open up Barcelona. Robinho finds Ibrahimovic, who threads a delightful pass through to Nocerino, who waits for Valdes to come out before firing beyond him and into the bottom corner. Game on.
Barca are dictating the pace of the game, but Milan still look a threat on the break, on the rare occasions they have the ball.
Ambrosini is penalised for pulling back Fabregas some 35 yards from goal. Perhaps lucky to avoid a booking there.
Alves tricks his way beyond Antonini before Abbiati comes out bravely to gather and takes a whack on his thigh for his troubles.
Xavi finds Messi on the edge of the Milan box and he has the time and space to get his shot away but it is comfortable for Abbiati.
Busquests attempts to feed the ball through to Fabregas, but there is just too much on the pass and Abbiati gathers.
Nesta has to be alert to take the ball off Fabregas' toes after a great pass from Cuenca before Antonini completes the clearance.
Xavi's corner from the right goes all the way across the Milan box and Puyol is just unable to reach it on the stretch having lost his marker.
Quick break from Milan with Ibrahimovic straying just offside after good work from Seedorf and Robinho.
Cuenca takes on his man out on the left flank and fires over a low cross towards the lurking Messi, which Mexes has to be alert to hack away.
Boateng looks to get Milan back on terms as he bursts into the area on the left, but his attempted cut-back skews off his foot and behind for a goalkick.
Right into the bottom corner from Messi there to bring up his 50th UEFA Champions League goal, the youngest player to reach the milestone.
Antonini is penalised for bringing down Messi, who had earlier elected to pass to Xavi despite being well placed to shoot, with the Milan man booked.
Puyol goes to shoulder charge Boateng, but simply bounces off him. Great strength from the Milan man.
Barcelona keep the pressure on and Alves' next cross is just ahead of Fabregas at the far post. Milan's defence could be in for a busy night here.
Great chance for Messi, but he skews it wide! Superb movement from Barca as Alves' cross is clipped back into Messi's path by Fabregas, but he fires across Abbiati and wide of the far post.
Good deep cross from Seedorf is played back into the box by Nocerino, but Busquets is well placed to clear. Barca break immediately and Messi fires in a powerful low shot from the edge of the box which is straight at Abbiati. Good early pace to this game.
Ibrahimovic shows great power and purpose to burst into the box, before kicking the ball away from his right foot with his left as he goes to shoot, with Pique sliding in.
First shot of the night comes in from Iniesta, but after a neat interchange he atches at the shot and it goes well wide.
Alves brings down Seedorf near the halfway line and Milan are awarded the free-kick, which they play backwards before Nesta gives away a cheap throw.
Both Pep Guardiola and Massimiliano Allegri are out on the edge of the technical area as Barca ping the ball around in the early stages.
Pre-match handshakes between captains Puyol and Ambrosini. Tonight's referee is Bjorn Kuipers from Holland.
Someone at UEFA is having a joke, they've sent the tallest mascot out with Messi, and they're nearly the same height as the little maestro.
OK folks, kick-off is now less than five minutes away. Thanks for all your contributions so far - let's hope we're in for a good game!
And Tekeste agrees, saying: 'I expect 1-1 and AC Milan will go through, they may even win if Pato gets enough time in the game.'
Ed Guerra writes: 'I remember Milan scoring inside the 1st min and 90th min in Sept at the Nou Camp, and Pato's back on the bench too, 1-1.'
Opta stat No.4: Zlatan Ibrahimovic has scored five goals and delivered three assists in his seven Champions League appearances this season, but has been caught offside more often than any other player in the competition this season (19).
Opta stat No.3: Xavi has completed 327 passes in his three appearances against AC Milan this season. Barcelona have completed more than twice as many passes as AC Milan in this season's Champions League (6,608 to 3,217).
Opta stat No.2: Lionel Messi has scored 30 goals in his last 26 appearances in the Champions League for Barcelona, and 49 overall in this competition. However, Messi has scored just one goal in his seven meetings against Italian opponents in the Champions League - from the penalty spot against AC Milan in the group stage this season.
Opta Stat No.1: The team drawing the first leg at home 0-0 have a 33% chance of progression in the Champions League/European Cup knockout stage (34 progressed and 64 were eliminated). However, AC Milan have always managed to progress to the next round following a 0-0 at the San Siro in the first leg in the Champions League/European Cup knockout stage (three different occasions).
Zlatan Ibrahimovic is back at Camp Nou tonight, having spent a single season with Barcelona earlier in his career. The Sweden striker is a player who polarises opinion. I'm in the 'against' camp. (watch, he'll get a hat-trick tonight now)
David Catterall says: 'I hope Barca win, I hate slow ponderous Italian football.' Guess you missed Inter 5-4 Genoa at the weekend, then?
Sidhartha Kumar writes: 'Milan will go through in dying minutes, but Barcelona will dominate the match. 2-1 Milan.'
Liam Hogan says: 'Would love to see Milan go through but my money is on Barca, 2-0, with Cuenca and a Messi penalty!'
Aaron Williams reckons: 'I'd like to see Barca lose... But who am I kidding... Messi is going to score at least one and I can't see Milan getting more than one away from home especially not at the Nou Camp.'
Marvin Sinclair is hedging his bets as he writes: 'Barca are strong at the Nou Camp but Milan are capable of scoring an away goal.'
Aled Roberts is the first to get in touch and is, rather disappointingly, predicting a 0-0 scoreline after 90 minutes, with Barca to go through in extra time.
It is a simple equation for the reigning champions of Europe - they need to win to progress. A draw or an away win will see Milan through, while only a goalless draw will take us to extra time and penalties.
Barcelona were not impressed with the state of the San Siro surface during last week's 0-0 draw, with the pitch restricting their usual flowing pass-and-move game, but they will have no such excuses tonight on home turf at Camp Nou.
If you want to have your say on tonight's match, then drop me a line to firstname.lastname@example.org, or via Twitter @skysportsrobp and I'll publish a selection of the best prior to kick-off.
AC Milan: Abbiati, Abate, Nesta, Mexes, Antonini, Nocerino, Ambrosini, Seedorf, Boateng, Robinho, Ibrahimovic.
Barcelona: Valdes, Dani Alves, Pique, Mascherano, Puyol, Xavi, Busquets, Iniesta, Fabregas, Messi, Cuenca.
Good evening, and welcome to our live and interactive coverage of tonight's UEFA Champions League quarter-final second leg between two giants of European football.