It was the fourth straight win for the Bucks, who are tied with Chicago for the lead in the Central Division a quarter of the way through the season.
Cleveland has lost two in a row and has yet to defeat a division opponent in seven tries this year.
The Cavaliers closed within 70-68 with 5:26 to play, but Ellis outscored Cleveland 6-2 over the next 3 minutes to give the Bucks some breathing room.
Brandon Jennings made only 5-of-20 shots for Milwaukee, but he scored 16 points while Ersan Ilyasova had 11. The Bucks shot only 39 percent from the field, but forced 24 turnovers.