Erling Haaland's first-half double put City on course for a comfortable win but coach Pep Guardiola's satisfaction at a solid start was tempered by the injury to his Belgian playmaker.
The marauding Norwegian ended some stubborn West Ham resistance when he dinked a delicate chip into the net after 70 minutes to make him the highest scorer in a single Premier League season.
There had been concerns over Haaland's fitness ahead of his transfer after he missed 16 games due to injury for Dortmund last term, but the Norway international has missed only four for City this campaign.
Haaland, who joined City this season from Borussia Dortmund, has scored 42 goals in 37 matches in all competitions, but suffered a groin injury against Burnley on March 18, and pulled out of Norway's squad for their Euro 2024 qualifiers.
With Arsenal eight points clear of second-placed City, the champions need to take three from Juergen Klopp's side in the early kick-off to ensure the Gunners do not take their lead into double figures.
Haaland continued his incredible goalscoring form with two second-half strikes at Elland Road on Wednesday to reach 20 goals from just 14 appearances -- seven games faster than the next quickest player to reach such a goal tally.
Norway striker Erling Haaland is a "perfect fit" for Manchester City and Liverpool will have to find ways to limit his threat in attack in Sunday's Premier League game at Anfield, manager Juergen Klopp said.
Erling Haaland took his goal tally to an incredible 19 in all competitions this season with another double in Manchester City's 5-0 demolition of FC Copenhagen in Champions League Group G on Wednesday.
Erling Haaland has overcome injury issues that have hampered him in recent seasons and defended the Premier League club's decision to send a physiotherapist along with the striker on international duty.
Erling Haaland has been named the Premier League's Player of the Month for August after scoring nine goals in five games in a brilliant start to his career in England.
Erling Haaland grabbed an outrageous 84th-minute winner against his former club Borussia Dortmund as Manchester City came from behind with two late goals to seal a 2-1 win in Champions League Group G on Wednesday.
Arsenal maintained their perfect start to the Premier League season with a fifth consecutive win but Manchester City's new signing Erling Haaland stole the limelight with his second hat-trick in 6-0 romp over Nottingham Forest on Wednesday.
Two of Europe's leading strikers will take on their former teams as Manchester City's Erling Haaland faces Borussia Dortmund and Barcelona's Robert Lewandowski meets Bayern Munich after the Champions League group-stage draw was made on Thursday.
Seven times reigning winner Lionel Messi was not nominated for this year's Ballon d'Or for the first time since 2005.
Dortmund start the weekend second in the table and nine points behind runaway Bundesliga leaders Bayern Munich, but with a game in hand.
Borussia Dortmund coach Marco Rose said Saturday that injured star striker Erling Haaland will remain sidelined for Sunday's game against Borussia Moenchengladbach.
On Monday, the exact nature of the injury and the length of his absence were still unknown.
Haaland has ruled himself out of Borussia Dortmund's Bundesliga match against Augsburg on Saturday and is set to miss Norway's upcoming World Cup qualifiers.
Marco Rose says he will do everything to keep Bellingham and Haaland at the Bundesliga club as the young stars attract the attention of Europe's top clubs.
Haaland has scored 37 goals in 38 games for Dortmund this season in all competitions.