A last ditch Thiago Silva header rescued a point for AC Milan who drew 2-2 against reigning Champions League winners Barcelona in their opening Group H encounter here Tuesday. With just 24 seconds on the clock Pato exposed Barca's defensive frailties to score the fifth fastest Champions League goal ever in front of a stunned Nou Camp crowd. Barca were on the back foot but bounced back with Lionel Messi more often than not at their heart of their best moves. It was he who jigged through the Milan defence to set up Pedro Rodriguez for the equaliser and then after 50 minutes Villa appeared to have given them the win with a fine 30-yard free-kick. However in stoppage time Silva leapt highest to power home a corner to give Milan a share of the spoils. Barcelona had an experimental back-line with Gerard Pique injured and Carles Puyol not risked by coach Pep Guardiola. It meant two midfielders in Sergio Busquets and Javier Mascherano were at the heart of the defence while in midfield Seydou Keita came into the side with no place for summer signing Cesc Fabregas. It took less than a minute for Milan to crack Guardiola's tactical plan as Pato ruthlessly exposed the centre-halves lack of pace. The Brazilian burst passed both Mascherano and Busquets before slipping the ball under keeper Victor Valdes. After a sluggish draw against Lazio at the weekend, Milan approached the game cautiously with Massimiliano Allegri admitting a draw would be a good result. Few believed him when he said his team would go out to attack as the best form of defence but they did just that in the opening stages, playing with a high tempo. Milan may have been without the injured forwards Zlatan Ibrahimovic and Robinho but they continued to pose a threat with Pato's acceleration the key. Alves moved across from full back and was able to block him in front of goal and then in another raid right through the centre of the defence Pato laid the ball to Kevin-Prince Boateng who blasted over. Barca hung on and as they gradually gained more possession, Milan struggled to cope with the incisive runs of their forwards. David Villa hit the side netting from an acute angle but it was really Messi who was making the difference as is so often the case. Messi had had a couple of shots well saved by keeper Christian Abbiati and then the woodwork saved the Italians midway through the half. Milan's ageing team were finding it hard to keep up their early pace and movement and this was made worse with the loss of Boateng to injury just after the half hour mark. Barca finally found the back of the net minutes later when Messi dribbled passed a couple of defenders on the left of the box and crossed for Pedro to knock the ball into an open goal. The main concern for Barca going into the break was an injury to Andres Iniesta with the midfielder replaced by Fabregas. The home side maintained their pressure with Abbiati saving from Xavi Herandez but then the keeper could do nothing about a Villa free-kick from distance which found the top corner. With the lead Barca were able to pass the ball around comfortably in the middle of the park. Much of the pre-match talk had been about Mark van Bommel's confrontation with Iniesta after they last met in last year's World Cup final but the Dutchman hardly saw the ball for much of the game as was the case for his midfield colleagues. The Milan forwards had become little more than spectators in what was almost a recital in maintaining possession from the Catalans. That was until the 91st minute when in a rare foray forward saw Milan win a corner, from which Silva pounced to equalise.