Zlatan Ibrahmovic marked his return to action with a brace as AC Milan inflicted defeat on their great rivals Inter to continue their 100 per cent winning start in the Serie A.
The Swede was fit to start after recovering from coronavirus and with 16 minutes on the clock he had already scored twice.
After winning a penalty, Ibrahimovic's spot-kick was saved by Samir Handanovic but he made no mistake with the rebound. And three minutes later, the 39-year-old capped a fine team move with a back-post finish from Hakan Calhanoglu's cross.
In contrast, Inter were missing no fewer than six players to Covid-19, including defenders Ashley Young and Milan Skriniar. In their absence, Antonio Conte's side were fragile at the back.
But in attack, Romelu Lukaku continued his fine goalscoring form to half the deficit and spurned another opportunity as Inter's fightback began.
And in the second half, Lukaku thought he had won a penalty only for VAR to overrule the referee's decision as the Belgian was adjudged to be in offside position.
Inter had their chances before and after that flashpoint, with Hakimi breaking the offside trap only to head off-target and Lukaku stabbing wide in stoppage time.
Victory gives Milan 12 points after four games, three points ahead of second-placed Atalanta, while Inter are five points behind in sixth-place.
TALKING POINT - AC Milan underline title credentials
It is now 20 games unbeaten for Stefano Pioli's side, a run that dates back to last season. Milan started the game with a perfect record after victories over Bologna, Crotone and Spezia, but this was their first real test and one they duly passed.
Inspired by the ageless Ibrahimovic, the Rossaneri recorded their first Serie A victory in the Derby della Madonnina in four years. Ibrahimovic was ruthless in attack, but this was a team performance that shone a light on a winning spirit missing for too long, even if they did ride their luck at times.
With serial winners Juventus in transition, this season is an opportunity for Milan to reclaim their crown. Victory over their arch nemesis will only strengthen their belief.
MAN OF THE MATCH
Zlatan Ibrahimovic (AC Milan): The veteran striker showed no sign of fatigue as he recovered from Covid-19 in another vintage performance.
Inter: Handanovic 6, D'Ambrosio 6, De Vrij 6, Kolarov 5, Hakimi 6, Vidal 7, Brozovic 5, Perisic 6, Barella 6, Lukaku 8, Martinez 7.. subs: Sanchez N/A, Eriksen 5.
AC Milan: Donnarumma 7, Calabria 7 Kjaer 8, Romagnoli 7, Hernandez 6, Kessie 7, Bennacer 7, Saelemaekers 7, Calhanoglu 8, Leao 7, Ibrahimovic 9.. subs: Tonali N/A, Krunic 5, Castillejo 5.
13' - GOAL! Inter 0-1 AC Milan (Ibrahimovic): Ibrahimovic sees his penalty saved by Handanovic but the Swede slots in the rebound!
16' - GOAL! Inter 0-2 AC Milan (Ibrahimovic): That man Ibrahimovic again! He finishes off a flowing team move! Calhanoglu releases Leao down the left and he whips a low cross to the far post where Zlatan buries it! Two goals in three minutes have Milan flying!
29' - GOAL! Inter 1-2 AC Milan (Lukaku): Lukaku to the rescue! Inter have one back! Perisic drives down the left flank and although Donnarumma gets a touch to his low cross, the ball falls into the path of the Belgian who is perfectly positioned to finish.
45'+2 - Miss! Lukaku is left completely unmarked as Vidal's corner is delivered. But the Belgian somehow glances his header well wide! A let off for Milan!
60' - Glorious chance! Vidal floats a perfect cross to the back post and picks out Hakimi who breaks the Milan offside trap. But with a diving header he misses the target!
90'+3 Close! Martinez lifts a pass into the path of Lukaku, who stabs wide! Milan survive, just. In this form, you would expect him to score!
- AC Milan have won each of their first four Serie A games for the first time since 1995/96 under Fabio Capello.
- Milan have scored in 24 Serie A matches in a row for the first time since 1973 (when they reached 29).