The Frenchman broke the deadlock just before the hour mark with a superb curling strike beyond the sprawling Kasper Schmeichel, his first goal for the club with his weaker right foot.
With 16 minutes remaining, City made it two through Gabriel Jesus, who poked into an empty net after Raheem Sterling squared the ball inside the box.
Before the opener, City had some great chances to get ahead but De Bruyne was satisfied to see Mendy do the honours.
"They played defensive and we had to be patient. That's what we did and I was happy for Mendy to break the deadlock," he said.
"I thought we were really good today. Especially the first half we totally dominated. They had the chance with Vardy but in the first half there was basically one team playing.
"If you look at 90 minutes it was 2-0. I think we deserved more goals. After an international break, that’s really well done by the team."
Pep Guardiola made six changes to the starting line up from our last match against Everton in the FA Cup and De Bruyne felt that it was good to freshen the team up, especially after a number of the players reported for international duty.
"I came back on Tuesday after the game and trained on Thursday and half the team trained yesterday.
"All we can do is rest up, be ready for the games and the manager chooses the players who have been here the longest.
"When you win the game it’s always the right pick. The team did really well and I am really pleased."
The Belgian was unlucky not to get his name on the scoresheet too as his free-kick in the first half cannoned back off the crossbar, but he did play an instrumental part in the victory, expertly playing through Jesus before the second goal.
The midfielder admitted that he enjoys contributing in any way possible.
"I am here to provide for the team," he said. "If I can set my teammates up and they finish it then I am happy.
"It is one more win and it is good to get into the rhythm."