And Messi, of course, is born to be king. Surround him with three, four or five foes, each of them dwarfing him in size but not in sporting intellect or craft, and he will escape like a spider through a fisherman’s net.

Give him a sight of those white posts that frame the goal, and he scores once, then twice in the opening half to settle down any doubts that creep into the team. The first came when Messi looked over his shoulder, noticed that Stephan El Shaarawy was not moving with him, and skipped toward the penalty area.

Skipped is wrong. It implies haste, but there was no undue rush from Messi, and none was apparent in Xavi when he almost nonchalantly passed the ball. Ahead of Messi, closing in from all sides, were four men of Milan. The Argentine used them as a shield, and lofted the ball into the top angle of the net from 20 yards.

Easy if you are Messi. His second goal may have been fractionally offside, but he moved at a speed that deceives the eye, and he shot through the legs of Milan’s alarmed defender, Philippe Mexès.

Not only was the momentum now on the side of history, but the grass beneath the players’ feet was cut fine, allowing the ball to be moved as Barça likes it. Excuses do not enter the Catalan mentality, but the field at Milan’s San Siro was comparatively patchy, heavy and slow.

The Barcelona players heard from their coach, Tito Vilanova, while they were in their dressing room at halftime, Gerard Piqué confirmed after the match. What might he say that the senior players and the stand-in coach, Jordi Roura, had not worked out for themselves after hours and hours of studying what went wrong in the first leg? Vilanova, recovering in New York, had contributed, for sure. He and Roura had dropped to the bench the captain Carles Puyol. They sought a faster transition between defense and attack than Puyol, who will soon turn 35, can muster. Puyol’s replacement, Mascherano, was pivotal in the third goal.

He had been lucky when his misplaced header let in M’Baye Niang, but the young winger for Milan struck a post with the target wide open. Some 68 seconds later, Mascherano atoned with a marvelous interception — and from him, via Iniesta and Xavi, the ball was swiftly recycled toward the right.