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 past six games against the Celtics.
"Our eyes are on winning a championship," Butler said. "Hopefully we get Gilbert [Arenas] back by March and when he comes back we will be even more dangerous."
Boston lost consecutive games at home and overall for the first time all season and dropped to 30-6. The Celtics are 2-3 over their past five and have averaged 85 points in that span.
Eddie House scored his only five points of the game to give the Celtics their largest lead at 77-63 with 6:24 left 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 layup by Butler and foul shot after he was fouled by Kendrick Perkins.
On the ensuing possession, Kevin Garnett failed on a three-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 layup as he beat Pierce off the dribble with 19.6 seconds left.
Lakers 123, SuperSonics 121 -- Kobe Bryant scored 48 points, including a jump shot with 4.3 seconds left, to lift Los Angeles past host Seattle in overtime.
Bobcats 119, Nuggets 116 -- Gerald Wallace scored 40 points, Matt Carroll hit two free throws with 4.6 seconds left, and host Charlotte made the big plays down the stretch this time in a win over Denver. Carmelo Anthony (Towson Catholic) had 35 points for the Nuggets.
Spurs 89, 76ers 82 -- Manu Ginobili scored 14 of his 20 points in the fourth quarter to lead San Antonio over visiting Philadelphia.
Consecutive games Atlanta had lost to Chicago before its 105-84 win Sunday. The Hawks had not beaten the Bulls since April 9, 2004.