City soon eased into the ascendancy at Etihad Stadium as Joao Cancelo and Manchester derby hat-trick hero Phil Foden struck in a first half where a tepid Southampton offered little.

Riyad Mahrez stretched the advantage after the break before Haaland collected his 15th league goal, as many as Kevin De Bruyne managed when finishing as City's top scorer in the competition last term.

Pep Guardiola's team moved two points clear of Arsenal, which plays Liverpool on Monday (AEDT), after a ninth straight home win in the league, scoring at least three goals in each of those games.

Former City goalkeeper Gavin Bazunu parried away a fizzing Mahrez half-volley, while Haaland struck the left post after a Foden throughball in a frantic start.

Cancelo broke the deadlock in the 20th minute as he twisted past James Ward-Prowse before drilling a left-footed strike past Bazunu, who then denied Foden on the half-hour mark.

However, there was no stopping Foden shortly after as the England international delicately chipped over the onrushing Bazunu following De Bruyne's pass.

Mahrez volleyed in a third goal from Rodri's lofted cross shortly after half-time, before City had a penalty appeal turned down for what they thought was a Mohammed Salisu pull on Haaland.

Southampton could not keep Haaland quiet for much longer, with City's new talisman converting into the bottom-left corner in the 65th minute after Cancelo's cutback.

Haaland has taken to life in England with ridiculous ease, scoring 20 goals in 13 games across all competitions and breaking numerous records along the way.

After just nine Premier League games, the striker needs just one more goal to surpass City's top scorer last season, De Bruyne, which is frankly astonishing.

He missed a few chances here, though, and looked on in disbelief when his shot that rattled the left post did not bounce into the net off the upright.

City heads to Copenhagen to play in the UEFA Champions League on Wednesday (AEDT), before the crunch clash at Liverpool arrives next Monday (AEDT), when Southampton hosts West Ham United.