Lautaro Martinez scored the only goal as Inter Milan beat city rivals AC Milan at the San Siro.
Second-placed Inter remain 13 points behind Serie A leaders Napoli, who won 3-0 at Spezia earlier in the day.
Captain Martinez headed in the game’s only goal from a corner kick by former Milan midfielder Hakan Calhanoglu.
Inter were disallowed two goals late – substitute Romelu Lukaku’s effort was ruled out for a foul on Malick Thiaw and Martinez’s strike for offside.
A lengthy decision by the video assistant referee upheld the decision to rule out Argentina striker Martinez’s effort because he was offside when he ran on Lukaku’s film on his way home.
Milan, who fell to sixth place in Serie A at the weekend, have lost five of their last six games in all competitions.
Stefano Pioli’s side only managed a shot on target in the 75th minute when Andre Onana denied Brahim Diaz.
The title remains firmly in Napoli’s hands thanks to their comfortable win in Spezia, with Georgia winger Khvicha Kvaratskhelia converting a penalty and Nigeria striker Victor Osimhen scoring twice.