Henrikh Mkhitaryan scored twice to help Inter Milan crush neighbours AC Milan 5-1 in Serie A on Saturday and continue their perfect start to the season.

Inter, who won their first three matches without conceding a goal, moved two points clear at the top of the standings on 12 points from four games.

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They are two points above second-placed Juventus, who beat Lazio 3-1 on Saturday, and three clear of Milan in third before they travel to Real Sociedad in the Champions League on Wednesday.

Mkhitaryan, Marcus Thuram, Hakan Calhanoglu and Davide Frattesi were all on target for Inter, securing their fifth consecutive win in the Milan derby across all competitions for the first time in history.

"Last year, four derby wins brought us a [Coppa Italia] trophy and allowed us to play in a very important [Champions League] final," coach Simone Inzaghi told a press conference.

"[Today's victory] gives us first place, but the championship is still very long."

Mkhitaryan struck from close range to put Inter in front in the fifth minute and new signing Thuram doubled the advantage before the break with a fine shot into the top corner for his second Serie A goal.

Milan pulled one back just before the hour mark through Rafael Leão, who latched onto a pass and shot past Inter keeper Yann Sommer as a sudden downpour of rain struck the San Siro.

Inter allowed Stefano Pioli's side control of possession but were far more ruthless and Mkhitaryan made it 3-1 in the 69th minute before midfielder Calhanoglu added the fourth from a penalty awarded for Theo Hernández's foul on Lautaro Martínez.

Substitute Frattesi completed the rout in stoppage time when he was fed by Mkhitaryan and the 23-year-old outwitted the goalkeeper to find the back of the net.

United States star Christian Pulisic started the game but was replaced after 56 minutes, while his international teammate Yunus Musah was brought on as a late substitute.

"A derby lost like this weighs a lot. I'm really sorry, especially for the fans," Milan defender Simon Kjaer told DAZN.

"Tonight they were smarter than us, we [only] played until 3-1."