The Reds were reduced to 10 men just before the break when Mane's boot collided with the head of City keeper Ederson, an incident which saw the Brazilian leave the pitch in a neck brace.
City went on to tear apart Jurgen Klopp's side and claim a 5-0 victory and despite a debate over whether Mane should have seen red, De Bruyne thinks that the severity of Ederson's injury meant that it was warranted.
"After the first goal we took control and then that happened," he is quoted as saying by the Manchester Evening News. "It was not a bad foul but with the way Eddy comes out of it, it's normal for a red card. If he doesn't have the injury it's a yellow card."
On the victory overall, he added: "I think we played really smart. We didn't give Liverpool time and if you score a few goals it makes it a lot easier.
"I think it was good to score a lot of goals. Obviously, it was different with them playing with 10 men and you have to keep your shape and be very focused.
"I think it's very good for the guys to get another game under our belt as the calendar is getting very busy so everybody will play."
The result leaves City second in the Premier League table, level on points with leaders Manchester United.