A brace from Lautaro Martinz and a goal from Romelu Lukaku sealed the deal for the Nerazzurri, who claimed the spoils in the Derby Della Madoninna for a second consecutive time.
Having ceded the pole position following a stunning loss to Spezia last weekend, the Rossoneri had to win in order to go top again.
However, a flat performance from Stefano Pioli's side meant Inter Milan cruised to a comfortable win, and are now genuine favorites for the Scudetto.
Here are the hits and flops from the Milan derby:
Hit: Romelu Lukaku (Inter Milan)
Romelu Lukaku continued his incredible record against AC Milan with another strike tonight, even surpassing Cristiano Ronaldo atop the league's scoring charts.
The strapping Belgian first set up Lautaro Martinez for the opener, laying a wonderful over-the-top cross for the Argentinian to head home from close range.
After he doubled Inter Milan's advantage in the second half, Lukaku put the final nail in the Rossoneri's coffin with a thumping low drive beyond Gianluigi Donnarumma.
That was his fifth strike against them in five games since joining the Nerazzurri, having struck at least once in every game, and Milan must be sick at the sight of him by now.
Flop: Zlatan Ibrahimovic (AC Milan)
The veteran striker was on target against Inter Milan in his last two appearances this season. Tonight, however, Ibrahimovic was below his best, failing to score against his former side.
With the 'away' side dominating possession, the Swede was isolated upfront, devoid of proper service and reduced to a mere bystander as his side was put through the gauntlet.
It's not to suggest the 39-year old failed to muster a single effort on target. In fact, he made five in the game, more than anyone, but his shots lacked the usual venom.
To make it worse for him, Lukaku was on target once again, rubbing salt into Ibrahimovic's wounds who was subbed off just moments later.