Mauro Icardi's stoppage-time header gave Inter Milan a 1-0 win over AC Milan in the city derby but they could be left counting the cost of that victory after key midfielder Radja Nainggolan limped off in the first half.
Nainggolan hurt his ankle in a crunching tackle with Lucas Biglia and the former Belgium international is now a doubt for Wednesday evening's (Thursday morning AEDT) UEFA Champions League match at Barcelona.
Inter have made a habit this season of scoring late goals and they did so for the fifth game this campaign when Icardi headed in Matias Vecino's cross, just as the match seemed certain to end goalless.
The Derby della Madonnina was - as always - eagerly anticipated and even more so with both teams coming into the match on hot streaks.
Inter had won six straight between Serie A and the Champions League while Milan were on an eight-match unbeaten run between Serie A and the UEFA Europa League.
However, in a game of few clear chances, both sides appeared lethargic at times - especially during the second half. Both teams did have a goal disallowed while Stefan de Vrij hit the post for Inter.
Inter thought they had taken the lead in the 11th minute and Icardi celebrated as music was played over the stadium tannoy but it was ruled out for offside.
Inter had the better chances and Matteo Politano's effort was deflected narrowly past the upright while Milan goalkeeper Gianluigi Donnarumma did well to palm Ivan Perisic's header around his left post.
De Vrij went even closer but his volley came off the right post with Donnarumma stranded.
Milan had barely enjoyed a sight of goal before Mateo Musacchio had the ball in the back of the net three minutes from half-time but it was ruled out for offside.
Vecino should have broken the deadlock moments later and the Uruguay midfielder had his head in his hands after ballooning the ball over from a great position.
The second half was an even cagier affair although Milan almost gifted Inter the lead when Biglia played a poor backpass, which took Donnarumma by surprise and the goalkeeper had to scramble to clear it.
Gian Piero Ventura's return to coaching could hardly have gone worse as his Chievo team were humiliated 5-1 at home by Atalanta.
Ventura was hired by Chievo during the international break, replacing Lorenzo D'Anna. It's the first job for the 70-year-old Ventura since he was fired as national coach nearly a year ago for Italy's failure to qualify for the 2018 FIFA World Cup.
Marten de Roon opened the scoring, Josip Ilicic scored a hat-trick and Robin Gosens netted the fifth before Valter Birsa converted a penalty for Chievo late on.
Chievo defender Federico Barba was sent off six minutes from half-time after a second yellow card.
Chievo's only points have come from two draws and the squad is on minus-1 after being deducted three points last month for false accounting.
Fourth-place Lazio left it late before winning 2-0 at Parma.
Ciro Immobile converted a penalty nine minutes from time and Joaquin Correa sealed the result deep in stoppage-time.
At the other end of the table, newly-promoted teams Frosinone and Empoli shared the spoils in a 3-3 draw, which left both sides in the relegation zone.
Bologna remained two points above Empoli after coming back from two goals down to draw 2-2 against Torino.
Elsewhere, Fiorentina drew 1-1 at home to Cagliari.