Watch: Red-hot Haaland toys with United, records historic hat-trick
The 22-year-old is now the first player ever to score hat-tricks in three consecutive Premier League home games. Through just eight league matches, he already has 14 goals on the campaign.
After scoring a rapid first-half brace, the Norwegian sharpshooter added to United's misery with a left-footed strike in the 64th minute to give City a 5-1 lead at the time.
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Phil Foden recorded his own hat-trick minutes later for the reigning Premier League champions.