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, 2-0 winners at home Saturday against Catania, thanks to a 2-1 win away to Chievo.
Lazio's third place, however, is now under threat after a 3-2 reverse at Genoa which left Vladimir Petkovic's side only three points ahead of Milan and Inter Milan, with Fiorentina, in sixth, a further point off the pace.
As Inter dropped more points in a shock 3-1 defeat away to Siena, city rivals Milan stole the limelight thanks to a Balotelli double on what was the 22-year-old's debut following his transfer from Manchester City in midweek.
Balotelli, a former Inter Milan player, told the media on his presentation Friday evening he had come to Milan "to help the club win trophies".
After seeing a drive whizz just past the post on 35 seconds it took him just 25 minutes to show fans of his intentions when he latched on to a through ball to smash the ball past Daniele Padelli in the Udinese goal.
Udinese pulled level in the 55th minute when Giampero Pinzi beat Marco Amelia in the Milan goal after being set up by Colombian Luis Muriel.
However, Balotelli made sure of all three points in the fourth minute of injury time when he beat Padelli from the spot after the referee deemed Thomas Heurtaux's challenge on Stephan El Shaarawy to be a foul.
"It's a great feeling to score, but I have to keep on going," Balotelli told Sky Sport.
"I'm very happy despite the fact I'm just getting over what has been a difficult period. I didn't play a lot (at City) and I could feel it in my legs. But tonight I was relaxed and I was ready.
The win will send shivers through the Nerazzurri side of Milan, especially in light of Inter's shock defeat to Siena.
In four minutes of first-half madness, Nigerian-born Swiss international Innocent Emeghara put the home side in front on 21 minutes before Antonio Cassano swiftly equalised, only for Alessio Sestu to restore Siena's lead on 24 minutes.
Alessandro Rosina then made the points safe with a 55th minute penalty that lifted Siena off the foot of the table above Palermo, who suffered a 2-1 home defeat to Atalanta thanks to goals from Chilean midfielder Carlos Carmona and Argentine German Denis.
In Verona, former France international Nicolas Anelka, a recent signing from Shanghai Shenhua, had barely taken his seat on the bench when Antonio Conte's side took a 10th-minute lead through Alessandro Matri, who cracked in a superb volley after good work from Arturo Vidal.
Stephan Lichtsteiner made it 2-0 three minutes before the break when Sebastian Giovinco played him through with a cheeky flick.
Midtable Chievo fought back and Cyril Thereau reduced the arrears seven minutes after the restart with a low drive but Juve held on for the win to move on to 52 points from 23 games.