Joao Cancelo, Phil Foden and Riyad Mahrez were also on target for the English champions, who move two points ahead of Arsenal at the top of the table.
City travel to Liverpool next weekend for what has become the Premier League’s marquee clash in recent seasons.
As it happened: Man City vs Southampton
But on this form Pep Guardiola’s men look unstoppable with Haaland added to a squad that has already won four titles in the last five seasons.
After a couple of early season slip ups, City are beginning to hit their stride in a six-game winning run and have now struck 31 goals in seven games at the Etihad this season.
The surprise was that for once Haaland was not leading the charge as the 22-year-old’s streak of hat-tricks in home Premier League games came to an end at three.
FULL-TIME Man City 4-0 Southampton@ManCity run out comfortable winners with goals from Joao Cancelo, Phil Foden,… https://t.co/4F7eYxzt5S
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Haaland should have opened the scoring when he rattled the inside of the post from Foden’s through ball in the early stages, but it appeared only a matter of time before the floodgates opened.
Cancelo was retained at left-back despite the absence of Kyle Walker at right-back and the Portuguese produced a finish Haaland would have been proud of as he marauded forward and fired into the bottom corner on 20 minutes.
Foden netted his first hat-trick as City tore Manchester United to shreds last weekend and continued his fine form in front of goal with a delightful chip over Gavin Bazunu.
Southampton boss Ralph Hasenhuttl could have taken charge of the Saints for the final time with reports this week that the Austrian is on the brink of being sacked.
After a bright start to the campaign, Southampton have lost their last four games and had no answer to the wave upon wave of City attacks after the break.
Guardiola has had some stern words for Mahrez on his physical conditioning in the early weeks of the season, but there were sparks of the Algerian’s best as he volleyed home Rodri’s cross to kill off the encounter as a contest.
All eyes then turned to Haaland’s quest to keep his incredible scoring streak going.
Twice the former Borussia Dortmund striker was guilty of passing up chances he would normally bury as he failed to connect with De Bruyne’s cross from point blank range and then failed to beat Bazunu on a one-on-one.
However, Haaland did finally net for the 10 consecutive club game when he fired home a low cross form the excellent Cancelo.