Inter conceded three goals for the second time in a week as AC Milan demolished their local rivals 3-0 at San Siro.
Goals from Alex, Carlos Bacca and M'Baye Niang handed the Rossoneri a third successive home victory in all competitions and avenged Milan's 1-0 defeat to their rivals in the corresponding Serie A fixture back in September.
For Roberto Mancini's side, it was another chastening experience after their 3-0 hammering by Juventus in the Coppa Italia in midweek and a fourth game without a win in the league.
Alex gave the designated hosts the lead with his second goal of the season in the first half, before Inter coach Mancini was sent from the touchline by referee Antonio Damato early in the second period.
Mancini watched from the stands as Mauro Icardi fluffed the chance to equalise from the penalty spot before Bacca turned home his fourth goal in as many matches and Niang completed the rout for a rampant Milan side.
Such a scoreline was barely conceivable early on as Inter started the match the better of the two teams.
Debutant Eder failed to turn home Juan Jesus' superb cross within six minutes, while Gianluigi Donnarumma had to leap to his right to keep out Marcelo Brozovic's 25-yard drive.
Juraj Kucka led Milan's response, twice twisting and turning into shooting positions without breaching the opposing defence as the match continued at breakneck pace throughout its opening quarter.
Stevan Jovetic's low drive was easily claimed by Donnarumma at his near post, while at the other end Miranda cleared Jucka's cross off the toes of Keisuke Honda and the two teams appeared to be heading to half-time deadlocked.
However, with 10 minutes left before the break, Milan found a way through Serie A's meanest defence. Honda swung in a cross from the right and Alex threw himself highest to nod beyond Samir Handanovic.
Mancini took exception to a challenge by Donnarumma on Eder in the early moments of the second half, with the Inter boss' protestations seeing him sent to the stands. The visiting coach was unhappy with Damato's failure to award his side a penalty but, with 20 minutes remaining, he got his wish.
Icardi's initial shot was well saved by Donnarumma but, when the ball rebounded to the Inter forward, Alex prevented him from taking a swipe at the loose ball. Icardi struck Donnarumma's left-hand upright from the spot, however, and Ivan Perisic was unable to guide home the rebound.
The miss proved costly. Within three minutes, Bacca put Milan out of sight.
Niang supplied a sensational cross from the right and Bacca lost Miranda before sliding home from eight yards out.
In the 77th minute, Milan added a third. Caught cold against the counter-attack, Inter's defence could only watch on as Niang converted at the second attempt after his first shot was saved by Handanovic.
The Inter goalkeeper produced a good save to prevent substitute Mario Balotelli - who was booked within a minute of coming on - scoring a fourth late on, but the damage was already done and Milan recorded their biggest derby victory since 2011.
Key Opta Stats:
- The last time AC Milan scored three goals in a Serie A derby was in April 2011.
- Milan have lost only one of their last nine Serie A matches (W4 D4).
- On the other side, Inter have won only one of their last six league games (D2 L3).
- The last 13 goals scored in the Serie A clashes between Milan and Inter have been netted by 13 different players.