The powerhouse Norwegian striker was not quite at his razor-sharp best as he missed several good chances before finally scoring his side's fourth goal in the 65th minute.
That took his tally to 20 goals in 13 games since his £51 million move from Borussia Dortmund.
The superb Joao Cancelo tormented the Saints defence before opening the scoring for the home side with a brilliant solo goal after 20 minutes. Phil Foden doubled the lead after 32 minutes and Rodri made it 3-0 just after half-time before Haaland completed the rout.
The win takes Pep Guardiola's side to the top of the table on 23 points, although Arsenal, who play Liverpool on Sunday, can overtake them if they win their game in hand at the Emirates Stadium. Mikel Arteta's side currently have 21 points from eight games.
You can see the player ratings from Saturday's game in the gallery above. To view the next image, click on the arrows or swipe if on a mobile device.