Ellis dueled with ex-Maverick O.J. Mayo down the stretch.
Dallas held a 81-76 lead late in the game, but Mayo pulled them to within two points with a 3-pointer.
Ellis responded with a jump shot 18 seconds later, again making it a two-possession game.
Mayo then hauled down an offensive rebound and followed with a layup, cutting the Mavericks' lead to two points with 2:47 left.
Mayo put in 28 points for Milwaukee.