Mario Balotelli scored a brace on his debut, including a controversial late penalty, to secure a precious 2-1 win for AC Milan over Udinese and move the resurgent Rossoneri up to fourth place in Serie A.
Champions Juventus remain top after restoring their three-point lead over Napoli with a 2-1 away win over Chievo.
Lazio's third place is under threat after a 3-2 loss at Genoa which left Vladimir Petkovic's side only three points ahead of Milan and Inter, with Fiorentina, in sixth, a further point behind.
As Inter dropped more points in a shock 3-1 defeat away by Siena, city rivals Milan stole the limelight thanks to a Balotelli double on what was the 22-year-old's debut following his midweek transfer from Manchester City.
Balotelli, a former Inter Milan player, said on Friday he had come to Milan "to help the club win trophies".
After seeing a drive whizz just past the post after 35 seconds, it took him just 25 minutes to show fans his intentions when he latched on to a through ball to smash the ball past Daniele Padelli in the Udinese goal.