Ronaldinho lived up to his predictions and scored his first ever goal for Milan since his summer move from Barcelona,as Milan inflict Jose Mourinho's first defeat on ten man Inter in an enthralling and explosive Milano Derby.
Milan came into this game in good form, having won their last three matches in all competitions. However, they were without the injured Alessandro Nesta, Pippo Inzaghi, Tabare Viudez, Andrea Pirlo, Philippe Senderos, and Marco Borriello. Carlo Ancelotti launched the Ka-Pa-Ro in an exciting looking attack, while Paolo Maldini, Marek Jankulovski and Massimo Ambrosini returned to the starting XI after being rested against Reggina in midweek.
Inter were coming off a four game winning streak, but they too had injury problems as Walter Samuel, Luis Jimenez, Maxwell, and Luis Figo were sidelined, with Sulley Muntari suspended. Nicolas Burdisso partnerred Marco Materazzi at centre back, while Mancini, Ricardo Quaresma and Zlatan Ibrahimovic formed the forward trident.
Inter had the first attempt of the game as Mancini picked up the ball 30 yards from goal, but he dragged his effort well wide of Christian Abbiati's right hand post.
Milan were having all the possession in the early stages, but their first effort didn't arrive until the tenth minute when Ambrosini's deflected long range shot looped harmlessly into Julio Cesar's arms.
Ibrahimovic got into a dangerous position inside the area, but his cross was kicked away by Abbiati, while Kaka asked for a Milan penalty when he received a nudge in the back in the box. It was an entertaining game, and Zambrotta charged forward from right back and unleashed a missile that finished not too far over.
On 16 minutes, Ibrahimovic would have been through on goal had he not had a very heavy first touch which allowed Abbiati to race off his line and dive on the ball.
Down the other end, Kaka's speculative effort fell to Pato inside the area, and his left foot snapshot appeared goalbound until it was charged down by Burdisso.
On 23 minutes Milan were agonizingly close to taking the lead as Kaka went on a mesmerising solo run, beating three men before laying the ball back to Ronaldinho, who saw his ferocious near post shot brilliantly turned around the post by Julio Cesar. It was a simply world class stop by the goalkeeper.
Pato was then put clean through on goal by Zambrotta's fine pass, but he was flagged offside in what replays showed to be a highly debatable decision.
On 36 minutes the deadlock was broken, and it was Ronaldinho who sent the San Siro into ecstasy with his first goal in a Milan shirt. Kaka found space down the right, and crossed into the middle for Ronaldinho's perfect header from the penalty spot into the top corner of the net. Inter players asked for offside but replays showed Materazzi playing Kaka level.
Rino Gattuso was fired up like never before, and he went into the book for a late foul on Quaresma, before having a ferocious touchline argument with Ancelotti, who had asked him to calm down.
Milan came looking for the second, and Pato skinned Christian Chivu, only for Julio Cesar to race off his line and come to the rescue. Kaka then went on another fine run, before going down under pressure from Materazzi, but the referee waved away the penalty appeals.
Into the second half and Ronaldinho still seemed to be enjoying himself as he took a ball down beautifully on the left before spraying the ball to Kaka on the right of the area, but the former Sao Paulo man blazed well over.
Mancini had been very quiet for Inter, but he had a decent opening on 51 minutes as he failed to make decent contact on a free kick curled in from the right.
Ronaldinho and Kaka were combining superbly at times, and the former found the latter, whose shot was deflected dangerously wide of the post. Ronaldinho then hit a snapshot off target from 25 yards, as did Kaka once again.
Jose Mourinho knew that changes needed to be made and, just shy of the hour mark, boldly brought on both Adriano and Julio Cruz for Materazzi and Mancini, thus forming a 4-2-3-1 formation.
Zanetti bombed forward from his new left back position, and crossed for Adriano, but the Brazilian's header was directed well off target.
Cruz went a little closer on 70 minutes, as he was afforded space to run at the Milan defence before firing wide. Ibrahimovic had a fine chance seconds later, as he ran unchallenged into acres of spaces, but he lashed the ball a couple of yards wide.
Ancelotti looked to tighten up the ship as Inter started to pile on the pressure, bringing on Mathieu Flamini for the tiring Pato.
Inter were on top now, but with 14 minutes remaining their hopes were hit when Burdisso received a second yellow card for a late foul on Kaka. With Materazzi off the pitch, Inter were now without both of their centre backs who started the game.
Kaka tried to take advantage of the one man advantage, and almost caught out Julio Cesar at his near post after another electric slalom. Mourinho then made his final change, introducing Dejan Stankovic for Vieira.
Stankovic almost scored with his first touch after a brilliant volley from the edge of the area that was beaten away by Abbiati, before Adriano fired the follow-up over.
Tensions were now high, and a touchline row erupted, which led to the departed Materazzi also seeing red. Goalscorer Ronaldinho left the pitch to a standing ovation soon after, with Andriy Shevchenko taking his place.
Milan were still looking for a second. Flamini was denied by Chivu at close range, before Shevchenko sliced his shot disappointingly from a promising position.
The Ukrainian went much closer with two minutes remaining, as his powerful drive was superbly tipped over the bar by Julio Cesar.
There was chaos in the Milan penalty area moments later, as Rossoneri players threw themselves in the line of fire as Adriano, Cambiasso and Quaresma all threatened to get shots in.
In the second minute of injury time Adriano had a glorious chance to equalise as he was left all alone at the back post just yards out on Maicon's cross, but he incredibly headed two yards wide.
Ibrahimovic then volleyed well over from the edge of the area, and Milan knew then that it was their day. Jose Mourinho suffers his first loss as Inter boss, and Milan are now well and truly back in the Scudetto hunt.
Milan: Abbiati, Zambrotta, Maldini, Kaladze, Jankulovski, Ambrosini, Gattuso (Bonera 87), Seedorf, Ronaldinho (Shevchenko 83), Kaka, Pato (Flamini 73)
Inter: Julio Cesar, Maicon, Burdisso, Materazzi (Adriano 58), Chivu, Vieira (Stankovic 80), Cambiasso, Zanetti, Mancini (Cruz 58), Ibrahimovic, Quaresma