Portugal winger Leao netted his third goal in as many league matches in the eighth minute at a sodden San Siro to move Milan up to second on 12 points from five games
Stefano Pioli insisted on Monday that AC Milan have turned their attentions to the Champions League opener with Newcastle United after the local derby humiliation at the weekend.
Belgium forward Lukaku rolled in Roma's sixth in the 82nd minute of a dominating performance in which talisman Paulo Dybala also got off the mark for the season with a brace.
Inter Milan laid down an early title marker on Saturday by handing out a 5-1 derby hammering to AC Milan and going it alone at the Serie A summit, while champions Napoli were held 2-2 at promoted Genoa.
Italy's Milan giants face off in Saturday's local derby which pits Serie A's form teams against one another in a match which will give an early indication of their title credentials..
Leonardo Bonucci has confirmed that he is taking legal action against Juventus, claiming that the Serie A club has not told the truth about their treatment of him after he was frozen out and eventually sold over the summer.
Inter Milan coach Simone Inzaghi has signed a new contract that will keep him at the club until 2025, the Serie A side said on Tuesday.
European heavyweights will be on their toes to execute eleventh-hour acquisitions as the summer transfer window for Europe's top five leagues is set to close tonight, from 10pm to 4am (Bangladesh Standard Time).
Right wing back Denzel Dumfries ran onto a cunning through ball by Marcus Thuram after 21 minutes and placed a low cross-shot past goalie Boris Radunovic