Adriano Galliani dubbed this 'The Derby of the World' between currently the best side on the planet and the club with the most international trophies in history. They hadn't crossed paths since the 2005-06 semi-final and their record was perfectly balanced at four wins each and three stalemates.
Zlatan Ibrahimovic, Robinho, Philippe Mexes, Taye Taiwo, Mathieu Flamini and the suspended Gennaro Gattuso were unavailable, so Antonio Cassano started with Alexandre Pato and Kevin-Prince Boateng. Barcelona's Carles Puyol was only fit for the bench and ex-Udinese star Alexis Sanchez sidelined, but Pep Guardiola opted for an all-attack formation with Pedro Rodriguez completing the trident. Javier Mascherano and Sergio Busquets formed an unusual central defensive partnership.
It took just 24 seconds for Milan to take advantage of this rather mismatched pairing, as Pato flicked it between them and burst forward with his notorious pace to coolly slot past the on-rushing Victor Valdes. It was the fifth fastest goal in Champions League history.
Barcelona kept possession in their usual style, as the visitors clearly focused on the counter-attack. A corner fell to David Villa at the back post, but he only hit the side-netting, while Pato was halted by a very tight offside decision when clear on goal again.
Christian Abbiati got down to beat Leo Messi's daisy-cutter round the post, but Pato drew away three defenders and rolled across to the unmarked Boateng, who blasted over. Seydou Keita then had to sprint back to intercept Pato again.
Messi curled a free kick over the wall and on to the top half of the near post at the 19th minute. Barcelona switched to three at the back to avoid the immense pressure they were under from Pato.
Villa volleyed over the bar and Abbiati parried from point-blank range as Dani Alves threaded through for Messi. Boateng had a back problem against Lazio on Friday that flared up again, so made way for Massimo Ambrosini. It pushed Clarence Seedorf into the trequartista role.
Alessandro Nesta was having a fantastic game and stood his ground to block Andres Iniesta's slalom in the box.
However, Barcelona did equalise when Messi drew three defenders to the by-line and somehow managed to squeeze a pass between them for the unmarked Pedro Rodriguez to tap in from three yards.
Iniesta also picked up an injury and was replaced by Cesc Fabregas. Dani Alves nutmegged Gianluca Zambrotta to release Messi, but the offside flag was raised. In first half stoppages a Thiago Silva error risked another counter, but Ignazio Abate stretched his neck for a decisive intercepting header.
After the restart Xavi's screamer stung Abbiati's palms for a corner. Sergio Busquets earned a very soft free kick for a nudge from Cassano, but with that set play David Villa curled a powerful right-foot strike into the near top corner to put Barcelona in front.
Nesta had to time his tackle perfectly to stop Messi's trademark run just as he was pulling the trigger from six yards. Urby Emanuelson replaced Cassano for a 4-4-1-1 system. Puyol made his comeback after knee surgery the day after the Champions League Final and Barcelona had 70 per cent of the possession.
Pato's weak header from a Seedorf corner kick was all the Rossoneri managed to create. Alberto Aquilani replaced Mark Van Bommel.
However, in stoppages Seedorf curled in a corner kick and Thiago Silva was far more reactive than those around him, soaring above a crowd of Barcelona players for a wonderful header.
Barcelona: Valdes; D Alves, Mascherano, Busquets, Abidal; Keita (Puyol 67), Xavi, Iniesta (Fabregas 39); Villa (Afellay 83), Messi, Pedro
Milan: Abbiati; Abate, Nesta, Thiago Silva, Zambrotta; Nocerino, Van Bommel (Aquilani 77), Seedorf; Boateng (Ambrosini 33); Cassano (Emanuelson 61), Pato
Ref: Atkinson (Eng)