AC Milan advanced to the UEFA Champions League quarter-finals for the sixth consecutive season but they needed extra time to secure a 1-0 victory over Celtic FC at San Siro.
Kaká finished clinically after a brilliant run three minutes into overtime, as the six-times European champions finally breached Celtic's resolute rearguard and silenced the vociferous away support.
The Brazilian had been involved from the start, bringing Artur Boruc into action on four minutes after Paolo Maldini had found Clarence Seedorf in space. Seedorf threaded a pass through Stephen McManus's legs to Kaká, whose curling shot was palmed away by the Poland goalkeeper. Undeterred, the visitors came forward and had a penalty appeal turned down when Jiří Jarošík's angled strike came off Maldini in the area.
Kaká was the key figure, though, and he put Marek Jankulovski through with a perfectly-timed pass which the midfielder cut back for Filippo Inzaghi at the near post, only for McManus to make a vital block. Milan's next move required another such intervention, as Inzaghi shaped to despatch Seedorf's cross but was denied by Lee Naylor.
Celtic advanced in search of an away goal yet were almost made to pay when Shunsuke Nakamura lost possession outside the Rossoneri box. The hosts broke in a flash, Jankulovski releasing Kaká down the left though the latter drove wide. Kaká was relishing his supporting role behind Inzaghi and was at the hub of everything Milan created, even conjuring a shot on goal from a prone position which was foiled by another goalline clearance on 37 minutes.
Seven minutes after the restart Inzaghi had his first attempt on goal. The impressive Jankulovski's left-wing run and cross warranted more but the angle was too tight for the veteran striker whose effort found the side-netting. As the game wore on, the Scottish champions ventured forward more and only the diving feet of Maldini prevented substitute Thomas Gravesen's half-volley flying goalwards. At the other end, the Italian outfit had two headers from Inzaghi cleared by McManus and Naylor.
Milan still dominated possession with Andrea Pirlo, Seedorf and Kaká weaving numerous intricate exchanges, although Celtic continued to hold firm with Boruc making comfortable stops from Pirlo and Massimo Oddo. Carlo Ancelotti's men spurned a great chance when Maldini's header was saved and he slipped at the crucial moment as the ball fell into his path with the goalkeeper prostrate. In a frenetic finale, Boruc brilliantly clawed a Seedorf free-kick away from the top corner, before Kaká's long-range strike rebounded off the bar.
Kaká had been threatening to score all game and his winner was worth the wait. After shaking off the challenge of Neil Lennon, he ran half the length of the pitch before slipping his shot through the legs of Boruc. Milan pushed for a two-goal cushion and Pirlo almost provided it from distance only for Boruc to save. Seedorf and Massimo Ambrosini also tried their luck but the honours went to Kaká.