Manchester City have beaten Newcastle comfortably, after an early scare.
Mitrovic scored a close range header, putting Newcastle a goal ahead against the Premier League's big spenders.
But Sergio Aguero responded with another header, drawing them level.
The Argentine striker then buried a deflected shot after a defensive error, and he completed his hat-trick just one minute later, after Kevin De Bruyne's through ball.
De Bruyne then scored himself, volleying home a Jesus Navas cross.
Aguero buried his fourth, bending the ball into the bottom corner. And he then poked in his fifth after a pass across the face of goal.
Steve McClaren has made one change to the Newcastle team that beat Chelsea last weekend.
Jack Colback is out with a calf injury, so Yoan Gouffran steps in.
Manchester City defender Pablo Zabaleta makes his first start of the season, while Eliaquim Mangala returns to the back line, and Fernando replaces the injured Yaya Toure in midfield.
Newcastle starting XI:
Krul, Janmaat, Mbemba, Coloccini, Mbabu, Sissoko, Wijnaldum, Anita, Gouffran, Mitrovic, Perez.
Man City XI:
Hart, Zabaleta, Otamendi, Mangala, Kolarov, Fernando, Fernandinho, Silva, Sterling, De Bruyne, Aguero.
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The Nigeria international struck on 10 and 28 minutes as he took advantage of some pitiful defending to give the promoted Hornets what proved to be a decisive lead.
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The Black Cats had hardly touched the ball before Callum Wilson scored his fifth Premier League goal of the campaign before a stunner from Matt Ritchie put them out of sight of Sunderland, who had defender Younes Kaboul sent off in the second half after the France international had been given the run-around by Wilson.
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