Goals from Gabriel Jesus, Sergio Aguero and Raheem Sterling saw Pep Guardiola's side to a comfortable win in Iceland, where the Hammers were caught cold. This is the final pre-season game for West Ham United and they are about to start their Premier League season with Manchester United next week Sunday.
City were dominant throughout the game, with new signing Ederson only facing one shot on his goal.
It was a fantastic display from last season's FA Cup semi-finalists who look sure to stake their claim at winning the Premier League for a third time this campaign.
Manchester City manager Pep Guardiola has urged the club to make even more signings during the summer transfer window, despite already spending roughly £200 million, while new Roma starlet Cengiz Under has admitted he was close to moving to the Etihad Stadium.
He said, "I think we need someone else, something else a little bit more, the transfer window finishes 31st August, we will see".
"We did the mistake very early in the game and then it's very hard".More news: Coroner Rules Prodigy's Death as Accidental Choking
"When we took the ball from them or when they lost possession, which was not very often, we could have opened them up because they play very high, and one proper and not very hard ball, we could have caused them problems, but we didn't and there was the difference".
"The players have to convince me", he added.
"We have to do that under pressure".
It took just 11 minutes into the second half for Aguero to get on the score sheet, moments after Edmilson Fernades nearly equalised for Slaven Bilic's side.
Guardiola then made seven changes to his side, including a debut for Bernardo Silva, but it was his namesake David Silva who was the next to come close when Hart got the faintest fingertip to a low drive across the face of goal.
"We have a lot of players with a lot of quality, that's why I'm so grateful for what the club has done", he said.