MILAN, December 23 (Serie A) - AC Milan goalkeeper Dida gave Internazionale an early Christmas present as his howler secured all three points for the Nerazzurri in the `derby della madonnina'.
Milan took the lead after 17 minutes through Andrea Pirlo's stunning free-kick before Julio Cruz levelled the scores in the 36th minute and Esteban Cambiasso was gifted his side's second on 63 minutes.
Inter are unstoppable in Serie A this season but the defending champions showed reverence to their city rivals as they welcomed the returning World Club Champions onto the pitch with a guard of honour.
They seemed to be showing the same deference in the game as both sides started cautiously before the match sprang into life just after the quarter-hour mark.
Milan were awarded a free-kick just outside the area which Pirlo, who played two seasons at Inter without scoring, fired into the top left corner giving Julio Cesar no chance.
Inter should have equalised just three minutes later as Cruz put a tantalising cross into the area.
Dida got a hand to it but could only watch from the ground as it fell to Luis Jimenez who saw his close-range effort crash back off the crossbar from a tight angle.
After 32 minutes, newly-crowned World Player of the Year Kaka almost doubled the Rossoneri's advantage as he dribbled half the length of the pitch into the area but found himself crowded out before he could get a shot in.
But four minutes later Inter drew level.
Cambiasso pulled the ball back to Cruz on the edge of the area who squeezed the ball through three Milan defenders and past the outstretched Dida into the bottom left corner.
Milan should have restored their advantage in the 40th minute but Massimo Ambrosini blazed it over from 22 yards leaving his team-mates - who had been screaming for the pass - furious.
A minute before the break Javier Zanetti almost gave Inter a deserved half-time but saw his shot fly agonisingly wide of the left-hand post, although Dida probably had it covered.
Milan came out in the second half in much the same way they'd ended the first - seemingly happy to sit back and soak up the pressure.
But the Rossoneri could have taken the lead five minutes after the break as Paolo Maldini's cross found Alberto Gilardino, who flashed his header narrowly wide of the left-hand post.
Inter should have gone ahead in the 57th minute as Cambiasso wasted a glorious chance - putting his shot well wide of the left upright from the edge of the area.
But six minutes later Dida and Maldini combined to gift the Nerazzurri the lead.
The veteran defender's poor clearance fell to Cambiasso at the edge of the area who scuffed his shot towards the centre of the goal.
Dida should have saved comfortably but the former Brazil keeper dived too far to his left and it somehow squeezed past him.
The goal seemed to deflate Milan and another Rossoneri goal seemed even less likely.
It was Inter who were controlling the game and they could have increased their lead in the 75th minute as Zlatan Ibrahimovic powered towards goal before unleashing a shot from the edge of the area which flew wide of the left upright.
Kaka came close to grabbing the equaliser in the 82nd minute as he hit a stunning volley towards goal but Cesar got down very quickly to parry.
Two minutes from time Ambrosini missed a golden opportunity to snatch a point for his side as he fired Serginho's shot wide from close range.
Elsewhere, Juventus complete the top three after their 2-0 success over Siena with goals from Hasan Salihamidzic and David Trezeguet.
Udinese lost ground on the leading trio after conceding a last-minute goal in a 2-2 draw against Empoli, while Fiorentina's 5-1 hammering of basement boys Cagliari saw former Chelsea striker Adrian Mutu score twice.
Lazio had Sebastiano Siviglia and Lorenzo De Silvestri sent off but battled to a 2-2 draw with Palermo.
Napoli drew 1-1 against 10-man Torino, with Livorno and Atalanta finishing with the same scoreline.
A hat-trick from Luca Vigiano helped struggling Reggina to a 3-1 triumph over Catania.