The Bucks, who have the worst record in the league this season, were nine points up at half time, but DeRozan led the Raptors' comeback for a 102-98 win.
The shooting guard told reporters: "We can't look at a team's record, come in here and think this is going to be a cakewalk. That team came out here and played extremely hard. They kind of blindsided us and we had to fight the whole game.
"We always find ways to fight through. We tried to turn up the aggressiveness, especially in the fourth quarter."
The Raptors play the Philadelphia 76ers on Wednesday.