City were made to work hard at some stages of the game, but eventually overran their Premier League opponents.
But Guardiola was very impressed with how the Saints approached the game, especially in the early stages.
"The first 20 to 25 minutes, they were the best team we've faced here," Guardiola said after the game.
"Only respect and admiration for Ralph [Hasenhuttl's] team.
"We suffered a lot to control them. We could not do good build-up because we could not contact with the holding midfielders. They were brilliant and today was won why the quality of the players we have.
"A tough game but one more victory. One game more we are 14 clear, nine games to play so Fulham - next one."