Wall's fast-break layup with 2:35 to play gave the Wizards their first lead, and after the Celtics tied it, Wall made his team's first and only 3-pointer of the game to put Washington ahead 84-81 with 58 seconds remaining.
Kevin Garnett made a layup to pull Boston within one, and Rajon Rondo stole the ball from Wall to give Boston a chance to win it. But Paul Pierce missed an 18-footer in the final seconds, and the Celtics' five-game winning streak had ended.
Wall finished with 16 points, six rebounds and four assists for the Wizards, who improved to 13-9 at home to counter their 0-20 mark on the road. Rashard Lewis had 18 points and 11 rebounds, and JaVale McGee added 16 points.
Garnett had 17 points for the Celtics, who shot 68 percent in the first quarter but 33 percent for the rest of the game. They especially went cold in the fourth, shooting 5-for-23 and scoring only 11 points — their lowest total for any quarter this season.
Ray Allen added 16 points, and Rondo had 13 points and nine assists for the Celtics. Boston played without Shaquille O'Neal, who didn't make the trip because of a sore right hip.
Early on, it appeared the Celtics wouldn't need O'Neal or much of an effort from any of their players. They led 35-20 after the first quarter and were outrebounding the Wizards 14-7. Rondo seemed able to drive anywhere he wanted on the floor.
But the Wizards had pulled within 10 at halftime. Then the same team that Wall claimed had "no heart" and "no fight" in the third quarter of an 18-point loss to Phoenix on Friday showed plenty of spunk and spirit in the same period against the Celtics. Washington started taking the ball to the paint and drawing fouls, and an 8-0 run fueled by free throws cut the lead to one.
The Celtics stretched the lead back to six, but Nick Young, who started 0-for-8 from the field, finally made a 15-foot runner that pulled the Wizards within two in the final minute of the third. Andray Blatche then tied the game at 70 the next time down, making a jumper with an assist from Mustafa Shakur, who was making his NBA debut after signing a 10-day contract earlier in the day.
The Celtics, who had controlled the game so smoothly in the early going, were out of kilter. Pierce sat down after picking up his fifth foul, and Allen missed an uncontested dunk. Glen Davis had a great chance at a garbage layup and missed — Boston's seventh consecutive missed field goal — then committed a frustration foul on the rebound.
Still, the Wizards couldn't take the lead, and the score was tied at 77 when Rondo made a driving layup to end Boston's 4 1/2-minute field goal drought with 4:24 to play.
But Wall's two big baskets finally put Washington on top, silencing a Boston-heavy crowd that gave Washington only its second sellout of the season.
Notes
The Wizards played without G Kirk Hinrich, who sprained his elbow in Friday night's loss. In need of a backup point guard, Washington signed Shakur from the D-League's Rio Grande Valley Vipers to a 10-day contract. Shakur's No. 22 jersey looked as if the numbers had been sewn on at the last minute by someone's mom — they weren't in the same location as his teammates' numbers. … Washington's sellouts have come against Miami and Boston. … O'Neal, injured in the first quarter of Friday night's win over Utah, sat out his 10th game this season. Coach Doc Rivers said he'll have an update on O'Neal when the Celtics resume practice Monday. "If it was something to be concerned about, I probably would have been told. So I'm just assuming that it's nothing that bad," Rivers said. Rookie Semih Erden started in place of O'Neal for the Celtics, who are missing Kendrick Perkins and Jermaine O'Neal with long-term injuries. … Hinrich will have an MRI to check for ligament damage. … The Wizards played back-to-back games at home for the was their first since November 2005.