Defender Danilo gave Pep Guardiola's side the lead with a fine 20-yard effort on 22 minutes.
“It was a great ball from Lowts. It was a tough finish because it just bounced in front of me and the keeper got a hand to it," said Gudmundsson after doubling his tally for the season.
“He was on great form today and made some really good saves, so I was just happy to see it hit the back of the net.
“We created some good chances and made their keeper work.
“In the first half from Ben he made a good save and so it's a credit to us that we made chances against a great team like Manchester City.
“I just want to get in the box and score some goals. That's two in the last five (league) games and I just want to keep the run going."