Lautaro Martinez scored the only goal as Inter Milan beat city rivals AC Milan at the San Siro.
Second-placed Inter are 13 points behind Serie A leaders Napoli, who won 3-0 at Spezia earlier in the day.
Captain Martinez scored the only goal of the game from a corner by former Milan midfielder Hakan Calhanoglu.
Inter had two late goals disallowed – substitute Romelu Lukaku’s effort ruled out for a foul on Malik Thiau and Martinez’s strike for offside.
A lengthy video assistant referee’s decision upheld the Argentina striker’s decision to disallow Martinez’s effort as he was offside when he ran Lukaku’s flick home to slot home.
Milan, who dropped to sixth in Serie A this weekend, have lost five of their last six in all competitions.
Stefano Pioli didn’t manage a shot on target until the 75th minute, when Andre Ona denied Brahim Diaz.
The title is firmly in Napoli’s hands thanks to a comfortable win in Spezia, with Georgian winger Khoecha Quartskellia converting a penalty and Nigerian striker Victor Oseimah scoring twice.
