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.
Cleveland got 26 points from Kyrie Irving and 17 from C.J. Miles.