Zack Steffen kept a clean sheet as the goalkeeper became the latest United States international to make his Champions League debut in Manchester City's win over Marseille.

Steffen got the nod to replace usual No.1 Manchester United on Saturday, and helped City to a 3-0 victory which was earned thanks to goals from Ferran Torres, Sergio Aguero and Raheem Sterling.

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Manager Pep Guardiola made nine changes in preparation for the first Manchester derby of the season but still closed out Group C with a fifth win from six games to finish with a club-record 16 points.

Ilkay Gundogan was substituted at half-time because of a minor ankle injury while Guardiola revealed Aguero will not start against Manchester United despite marking his return from injury with a goal.

"His instinct to score will always be there," said Guardiola about Aguero. "He had three or four training sessions and the reaction was good. He had 25 minutes and scored a goal so step by step."

It was Steffen's third start for City after returning from a loan spell in Germany with Fortuna Dusseldorf having playing in two Carabao Cup ties earlier in the season.

"I love shut-outs! The guys in front of me did a really good job in terms of limiting their chances and I didn't really have too much to do so kudos to the guys in front of me," Steffen told the club's website.

"We wanted to get the win and a shut-out to keep the confidence going ahead of the derby at the weekend."

"It's a big game and we're excited for it."

The 25-year-old, who made two saves, is one of a record 10 USMNT players who were named to Champions League squads for this season's competition alongside Christian Pulisic [Chelsea], Giovanni Reyna [Borussia Dortmund], Tyler Adams [RB Leipzig], Weston McKennie [Juventus], Sergino Dest [Barcelona], Konrad de la Fuente [Barcelona], Chris Richards [Bayern Munich], Ethan Horvath [Club Brugge] and Alex Mendez [Ajax Amsterdam], with nine making at least one appearance in the group stages.