Inter 1 Milan 0: Guarin sends Mancini's men top
Inter clinched the derby bragging rights against Milan as Fredy Guarin's strike gave them a 1-0 win at San Siro on Sunday.
The Colombian fired home just short of the hour mark as the Nerazzurri kept up their flawless start to the Serie A season in an open contest.
Luiz Adriano spurned two clear openings in the first half while Mauro Icardi - passed fit after a thigh injury to lead Inter's attack - should have done better when put clean through by Stevan Jovetic.
The returning Mario Balotelli had Inter worried in the second half and only the woodwork denied him a famous goal, but Guarin's fine effort proved to be the difference.
Victory puts Inter top of Serie A, while Milan remain 12th with just three points from as many games.
Luiz Adriano spurned a great chance just three minutes into the clash, Samir Handanovic saving well after the Brazilian was played in by Carlos Bacca, though Icardi fired narrowly wide from distance as Inter themselves started brightly.
A fine Giacomo Bonaventura throughball sent Luiz Adriano clean through once again after 16 minutes, but Jeison Murillo was across sharply to block.
The game began to turn scrappy as both sides struggled to retain control of possession, but Guarin should have done better when played through by debutant Ivan Perisic in one of Inter's better attacking moves.
Keisuke Honda had Handanovic at full stretch with a low drive, while Jovetic rasped an effort just past the far post and Icardi fluffed a shot straight at Diego Lopez when clean through as Inter finished the half the stronger.
Lopez's poor clearance handed Jovetic another chance shortly after the break but Cristian Zapata was able to close the space well.
Honda saw a shot deflected wide after some fine footwork from Carlos Bacca before Guarin forced Lopez to claw the ball over the bar as he headed down Perisic's cross.
But the Colombian found the net just three minutes later - and in some style.
Handanovic and Geoffrey Kondogbia almost made a mess of possession inside the Inter area but, after a quick break forward from Davide Santon, Guarin cut inside and unleashed a fierce drive into the far corner with his left foot.
Milan responded by bringing on Balotelli for the ineffective Bacca and the Liverpool loanee immediately had Inter nervous as Honda just failed to connect fully with his dangerous free-kick.
Balotelli rattled the post with a shot from distance and forced Handanovic into a save with a ferocious free-kick as Milan pushed for an equaliser.
Inter remained resolute, however, and extended their record to just one defeat in their last 11 designated home league matches against their city rivals.