A late goal from Rodrigo Palacio gave Inter Milan a 1-0 win over city rival AC Milan in an entertaining derby match in Serie A on Sunday.
Palacio struck four minutes from time to send three quarters of San Siro into a frenzy.
Andrea Poli had missed an open goal for Milan, while Inter had a strong penalty claim turned down shortly before halftime after a clumsy challenge from Cristian Zapata on Rodrigo Palacio.
Mario Balotelli, who spent a troubled few seasons at Inter before a move to Manchester City, had a number of chances against his former club.
Milan midfielder Sulley Muntari was sent off in stoppage time after he shoulder-barged Zdravko Kuzmanovic for time wasting.
"We were obviously tired in the last 20 minutes," Milan coach Massimiliano Allegri said. "I didn't manage to do my last substitution when I wanted to because the ball didn't go out. I don't have to reproach the lads for anything, Inter had a good game, especially defensively. I'm disappointed because it was a balanced game apart from in the last 20 minutes."
Earlier, league leader and two-time defending champion Juventus beat Atalanta 4-1 to maintain a five-point advantage over Roma, which eased to a 4-0 victory over bottom club Catania.
Milan slipped into the bottom half of the table. Inter is fifth.
"A derby is a derby but it was even more important to win after three draws and a bad defeat," Inter coach Walter Mazzarri said.
There was an odd atmosphere at San Siro ahead of kickoff as Milan fans had been banned from bringing in their pre-match choreography and Inter supporters had removed their banners too in a show of solidarity.
Riccardo Saponara started for the first time for Milan, having played just 24 minutes in two substitute appearances. Sapanora almost helped give Milan an early lead with a through ball for Balotelli, but Juan Jesus deflected the Italy striker's effort wide of the right post.
Both sides had opportunities but failed to really test either goalkeeper as Milan dominated for large periods.
Milan should have taken the lead just before the half hour mark when Inter goalkeeper Samir Handanovic flapped at a corner and the ball fell to Poli, who incredibly blasted over from 10 yards.
Balotelli had two good chances shortly after halftime but was first denied by a fine one-handed save from Handanovic before a volley was deflected narrowly wide.
Inter nearly broke the deadlock 10 minutes from full time but Christian Abbiati pulled off a double save to deny first Palacio and then Fredy Guarin.
Palacio scored shortly afterwards, flicking the ball in from six yards with a backheel from Guarin's pass.
Earlier, Juventus strolled to its ninth successive win. It got off to the perfect start when Arturo Vidal's pass was deflected into Carlos Tevez's path and he beat his defender before firing past Andrea Consigli.
Maxi Moralez levelled for Atalanta as Gianluigi Buffon conceded his first goal in 744 minutes of football. Incidentally, that matched exactly Roma goalkeeper Morgan De Sanctis' streak at the beginning of the season. Both are seventh on the all-time list.
Juventus restored its lead almost immediately after halftime. Fernando Llorente touched on Kwadwo Asamoah's cross for Paul Pogba to slide the ball in from close range.
Goals from Fernando Llorente and Vidal sealed the match.
In the capital, Roma captain Francesco Totti made his first start after almost two months out with injury.
Mehdi Benatia scored a double, either side of Mattia Destro's third goal in as many matches since coming back from several months out with injury.
Gervinho somehow failed to score in the 75th when Catania goalkeeper Alberto Frison parried a Totti effort into his path and the Ivory Coast forward, who was in acres of space with an empty net in front of him, incredibly hit the right upright from 10 yards.
He atoned for his error when he badly mishit Adem Ljajic's low cross but the ball bounced past Frison and into the back of the net.
Roma moved five points ahead of Napoli, which drew at Cagliari on Saturday. Juventus hosts Roma immediately after the winter break.
Fiorentina is three points behind Napoli after Rossi secured a late win eight minutes from time, taking advantage as the ball bounced off a Sassuolo defender before he fired it into the bottom left corner.
The American-born Rossi, who plays for the Italian national team, is the top scorer in Serie A with 14 goals, three more than Tevez.
Luca Toni scored twice as newly promoted Hellas Verona beat Lazio 4-1, while Torino also scored four goals as it came from behind to beat Chievo Verona 4-1.
Elsewhere, Sampdoria held Parma to a 1-1 draw, while earlier Alessandro Diamanti's powerful strike gave Bologna a 1-0 win over Genoa.