Ellis finished with 33 points, Brandon Jennings added 18, Drew Gooden scored 16 and Mike Dunleavy scored 13 for the Bucks, who pulled to within two games of the New York Knicks in the race for the Eastern Conference's final playoff spot.
Josh Smith pumped in 30 points and grabbed 18 rebounds for the Hawks, who came into the contest on a four-game winning streak.
Ivan Johnson provided 17 points off the bench for Atlanta.
Charlize Theron not engaged to Sean Penn 'yet'
Pistorius testifies he didn't consciously pull trigger when he shot girlfriend