Sulley Muntari's scrappy goal gave leaders Inter Milan a deserved 1-0 win over old rivals Juventus in a lively Serie A encounter on Saturday.
Inter, now four points clear at the top pending AC Milan's trip to Torino on Sunday, dominated at a packed San Siro to end third-placed Juve's streak of seven wins in a row in all competitions.
Ghana midfielder Muntari netted his first league goal for the club on 72 minutes after former Juve striker Zlatan Ibrahimovic scuffed an effort across goal.
The match is known as the 'derby of Italy' because of the fierce rivalry and it was given extra spice by some verbal spats between Inter coach Jose Mourinho and Juve's Claudio Ranieri, sacked by Chelsea in 2004 to make way for the Portuguese.
Mourinho sprang a surprise by starting with Brazil forward Adriano, who had been dropped for the previous four league games for breaches of discipline.
Inter again lacked shape in midfield but the champions quickly began to dominate, the referee waving away appeals for a penalty after the ball clipped Giorgio Chiellini's hand in the first minute.
Dejan Stankovic then found himself in space in the box but the ball became stuck under his feet and he wasted the first of a number of good chances for the hosts.
Ibrahimovic twice shot wide from good positions and Muntari forced goalkeeper Alex Manninger into two smart saves.
Juve, who won 2-1 at Inter last term, barely threatened although Marco Marchionni felt he had a penalty claim after going down under Muntari's challenge.
Julio Cesar also beat away Juve striker Alessandro Del Piero's header after Muntari had broken the deadlock on a chilly night.
Juve, whose 2006 title was stripped and handed to Inter after a match-fixing scandal, trail the leaders by six points.
In the day's early game, Riccardo Montolivo struck twice to help Fiorentina go fourth with a 4-2 home win over Udinese.
Early season pacesetters Udinese, who have now lost three league games on the trot, took the lead through a 20-metre strike from Antonio Floro Flores. Adrian Mutu's chipped penalty put the hosts level before Montolivo's double and Alberto Gilardino's tap-in took them clear.
Antonio Di Natale converted a late penalty for the visitors after Fiorentina's Gianluca Comotto was sent off for handling on the line.
Second-placed Milan meet Torino in Sunday's late game (1930) with the main programme of matches kicking off at 1400.