Caron Butler scored 21 and Washington beat Boston 88-83 on Monday night for the Wizards' second victory over the Celtics in three days.
"Our eyes are on winning a championship," Butler said. "Hopefully we get Gilbert back by March and when he comes back we will be even more dangerous."
Antawn Jamison added 20 points and 10 rebounds for the Wizards, who handed Boston its first two-game losing streak of the season.
Butler scored nine points during a 25-6 run over the final 6:24 of the fourth quarter to give the Wizards their fifth win in the last six games overall and against Boston.
"It's tough to lose at home," Celtics coach Doc Rivers said. "We let our guard down and had a chance to keep them down."
Boston also lost consecutive games at home for the first time all season and dropped to 30-6. The Celtics are 2-3 over their last five and have averaged 85 points a game over that span.
"As much as we preach defense, offensively I think we've hit a little snag," Celtics guard Ray Allen said.
Eddie House scored his only five points of the game to give the Celtics their largest lead at 77-63 with 6:24 remaining before the Wizards rallied.
Trailing by 14, the Wizards went on an improbable 19-4 run to take an 82-81 lead with 40.1 seconds remaining capped off by a Butler lay in and foul shot after being fouled by Kendrick Perkins.
On the ensuing possession, Kevin Garnett failed on a 3-pointer, but Paul Pierce was fouled on the rebound and sank both free throws to regain the lead for Boston at 83-82. Butler then responded with a high-arcing lay-up as he beat Pierce off the dribble with 19.6 seconds remaining.
Garnett failed on another chance to regain the lead for Boston when his turnaround jumper clanked off the back rim. Butler got the rebound and hit a pair of free throws for an 86-83 lead with 8.3 seconds remaining. After calling a 20-second timeout, the Celtics inbounded to Allen whose 3-pointer fell way short before DeShawn Stevenson clinched the game with two free throws.
"We always seem to come back strong when our backs are against the wall. We did it Saturday night and we did it tonight in a tough road game," Jamison said. "To beat these guys in back-to-back games considering how they've been playing is something special."
Washington shot a combined 37 percent in its two victories, but shut down the struggling Celtics offense. Brendan Haywood scored 14 points and grabbed seven rebounds and was very effective against Garnett.
Garnett led the Celtics with 23 points while Pierce added 18.
"We didn't stop playing, we just didn't hit our shots," Garnett said. "We need to fix things before Portland."
The Celtics struggled to a 37-35 halftime lead while shooting 43 percent. Stevenson led Washington with 11 while shooting 3-of-4 from beyond the arc, despite the Wizards shooting 35 percent overall.
Point guards Rajon Rondo and House combined to score nine points while shooting a combined 4-for-15 for Boston.
Jamison and Butler are the highest scoring forward tandem in the NBA averaging 43 points per game. ... Pierce has led the Celtics in scoring once in the last eight games. ... Butler extended his streak to 41 straight free throws made. ... Curt Schilling was in attendance and received a loud ovation during a third quarter timeout. ... Allen shot 8-for-27 in the two games against the Wizards.