Singleton nailed two free throws tying it at 86 before Rondo hit a 20-foot jumper from the top of the key to push Boston back in front.
Boston had taken a 71-60 lead with just over 10 minutes to play on Pierce's three-point play, coming on just his second basket of the game, when he was fouled on a fast-break layup. The Wizards then climbed back mostly behind the play of Singleton, who scored six of Washington's eight points as it narrowed the gap to 77-76 on Webster's 3 with 5:19 left.
After Terry nailed a 3 for Boston, the Wizards scored the next four points, tying it 80-all on Seraphin's dunk with 3 1/2 minutes to play.
The Celtics had trailed by seven in a first half that mostly featured poor shooting and sluggish play — except when Garnett was on the floor — but scored the initial five points after the break to tie the game at 42.
Garnett had 10 rebounds, two blocked shots and seven points in the first half and the Celtics outscored the Wizards by 11 when he was on the floor.
Washington pulled to a 49-44 lead midway into the third quarter on Beal's three-point play before Boston closed the quarter by scoring 12 of the final 14 points to grab a 66-58 lead entering the final quarter. Chris Wilcox, still working back into shape after heart surgery last season, sparked the run with six points and Terry had a pair of baskets.
Washington shot just 29 percent in the opening quarter and trailed 21-16 at the break, but used a 20-7 run midway into the second en route to a 42-37 halftime edge.
NOTES: Garnett had 10 rebounds in just his first 7:09 of play, collecting his 10th only 16 seconds into the second quarter. ... Wizards C Nene was out again with plantar fasciitis of his left foot. He hasn't played yet this season. ... Washington G Jordan Crawford, who tweaked his ankle in the loss to Boston Saturday, returned to action. ... The Celtics host Philadelphia Friday before playing four of five on the road. ... The Celtics were given a delay of game warning because Garnett wasn't ready for the tip, going through his usual pregame ritual when he goes under one of the baskets and slightly bangs his head against a padded support to get motivated.