Inter midfielder Hakan Calhanoglu scored a penalty against his former club Milan, who missed out on an opportunity to go top of Serie A in a 1-1 derby draw at San Siro.
Calhanoglu - who joined the blue half of Milan from the red side on a free transfer in July - won and then converted an early spot-kick, but Inter were pegged back soon after as Stefan de Vrij scored an own goal.
The Nerazzurri were handed a second penalty in the first half, but Ciprian Tatarusanu saved Lautaro Martinez's strike from 12 yards to keep his side level.
Inter looked the more dangerous side in the second half, yet were unable to secure the victory. However, simply denying Milan three points meant the title-chasing Rossoneri were unable to leapfrog Napoli, who also drew 1-1 with Hellas Verona.
Calhanoglu opened the scoring against his former club, earning a penalty from Franck Kessie before powering the spot-kick down the middle in the 11th minute following a lengthy VAR check.
Inter's lead did not last long, however, as De Vrij inadvertently headed into his own net past Samir Handanovic just six minutes later after losing the flight of a cross from the left.
Milan then conceded a second spot-kick, with Fode Ballo-Toure scything Matteo Darmian down in the box, but Martinez stepped up this time and Tatarusanu produced a superb save from the striker's well-struck effort in the bottom-left corner.
Inter twice looked certain to re-take the lead shortly before the break when Nicolo Barella's shot was hacked off the line by Ballo-Toure before Martinez fired narrowly wide.
The Nerazzurri continued to push for a second after half-time and created a number of chances, including Calhanoglu's fizzing effort across goal, which was missed by both Martinez and Edin Dzeko.
Substitute Alexis Saelemaekers struck the post and Kessie skewed the rebound wide in the Rossoneri's best chances to win the game late on, but ultimately neither side was able to find a winner in the closing stages.