The Etihad was left stunned within 22 seconds of the start, as John Stones failed to convincingly clear Keane Lewis-Potter’s header and Yoane Wissa took advantage to head in the earliest home goal City have ever conceded in the league.
The Bees continued on the front foot with Bryan Mbeumo almost getting the better of Rico Lewis before Nathan Collins’ instinctive effort was stopped by Ederson.
Despite City’s early struggles, they were back on level terms in the 19th minute when the ball fell to Haaland, whose first-time strike took a slight deflection off Ethan Pinnock and nestled inside the far post.
Pinnock then saw a header bounce behind off the crossbar but was outmuscled by Haaland shortly after as the striker latched onto Ederson’s long ball and coolly dinked it past Mark Flekken to complete the turnaround.
Savinho and Jack Grealish had a shot apiece denied but there was still another blow for Thomas Frank before half-time, as Wissa limped off following a challenge from Mateo Kovacic.
Pep Guardiola made two changes of his own at the restart - which included giving Rodri his first minutes of the season - and the hosts took control without initially giving Flekken a notable test.
Lewis-Potter was wasteful at the end of a blistering Bees counter, although Flekken remained the busier keeper as he pushed away Grealish’s curling effort and tipped Haaland’s strike over to deny the Norwegian his third consecutive hat-trick and keep his side in the match.
With the pressure continuing to build, Kyle Walker then grazed the roof of the net with a strike from outside the box before one Savinho effort was saved and another fizzed agonisingly wide.
Haaland then smashed the post, saw his follow-up blocked by Collins and was then denied by Flekken moments later, ensuring City’s 13th consecutive Premier League win was the first in that run to be decided by just one goal.
That can be a slight consolation for Brentford, as can the fact that their only two defeats from five competitive matches this term have come against Liverpool and now the reigning champions.
Flashscore Man of the Match: Erling Haaland (Manchester City)