The Pistons owned an 11-point lead going into the fourth period, but scored just 15 points in the final quarter as the Pacers made a run.
Wallace was fouled with four seconds left and his team leading by two, but he made only one of two free throws, giving Indiana an opportunity to tie.
Danny Granger wound up taking the three-point shot, but Wallace swatted it way as time expired.
The Pistons -- heading for the playoffs as the No. 1 seed in the Eastern Conference -- played the opener of a seven-game road trip. Indiana lost for the third time in four games.