Guardiola: Haaland helping to bring the best out of De Bruyne
Haaland got on the scoresheet in the 65th minute to grab City's fourth goal after first-half strikes from Joao Cancelo and Phil Foden plus a volley after the interval from Riyad Mahrez.
De Bruyne assisted Foden's strike to take his tally up to 11 assists for the season in all competitions, but Guardiola said the Belgian midfielder still has room to improve.
"For Kevin and players like him, especially Kevin, having this threat, this guy who can make movements in behind with this space helps a lot," Guardiola told reporters after the win.
"Kevin made plenty of assists, but he can play better. Today was not the best Kevin that we know, but of course, by himself he can put his mate in front of the keeper most of the time.
"But of course, if they have [Haaland] or Julian [Alvarez] or Phil [Foden] making movements behind, it's so important for players like Kevin."
The victory took City to the top of the standings on 23 points from nine matches although Arsenal, on 21, can reclaim the lead if they beat Liverpool at home later on Sunday.
City next travel to FC Copenhagen in the Champions League midweek before taking on rivals Liverpool in the Premier League on Sunday.