After scoring in his side’s 3-1 Premier League win against Everton last weekend, the 28-year-old maintained his form at the Etihad Stadium.
The former Leicester City forward set up Raheem Sterling’s goal in the 66th minute of the encounter before Phil Foden sealed the victory in stoppage time.
The win ensured Pep Guardiola’s men climbed to the top of the Group C standings with six points from two games.
Mahrez featured for the duration of the game while Nigeria’s Iyayi Believe Atiemwen replaced Bruno Petkovic with seven minutes left to play but could not help Nenad Bjelica’s men grab a consolation goal.
The Algeria international will look to continue impressing in their next outing against Wolverhampton Wanderers on October 6.