"Our Achilles' heel is that we'll fare well against the pretty good teams in the league -- we'll beat Dallas one day, then lose to the Bobcats," Jamison said. "We didn't want that to happen."
And it showed. Jamison scored 34 points to help Washington extend Boston's losing streak to 11 with a 105-91 win Sunday.
Caron Butler added 21 points and 11 rebounds, and Gilbert Arenas shrugged off a poor shooting night to finish with 23 points for the Wizards, who have won six of seven to move into first place in the Eastern Conference. Brendan Haywood added 11 points and nine rebounds.
The Wizards won in Detroit 99-96 on Friday to move a half-game ahead of the Pistons and into first place. The teams play again Tuesday, but the Wizards were careful not look ahead.
"We really took this game more serious than we did the Detroit game," said Jamison, who scored a season-high 35 Friday.
Following a first half in which there were 15 lead changes and 14 ties, Washington outscored Boston 57-41 in the second half to turn a 50-48 deficit into a route.
Butler, coming off a season-low eight points against Detroit, scored eight during a key 10-2 third-quarter spurt.
He split defenders for a layup in traffic to tie it at 59 with 6:06 left in the third. After the teams traded baskets, Butler made two free throws to put the Wizards up for good. He then scored on a breakaway that he started with a steal to give the Wizards a 65-61 lead.
Arenas missed eight of his first 10 shots before draining two shots late in the third quarter to help the Wizards extend their lead. The Celtics then pulled to within 77-71 early in the fourth, but Washington responded with a 24-9 spurt to run away with it.
"Coming off a tough win in Detroit, our whole thing was get it close, and in fourth quarter the veterans will take the game over," said Arenas, who was 6-of-16 from the field with six assists. "And that's what we did. We hit big shots and made big plays at the end."
Delonte West had 22 points and 11 assists and Ryan Gomes scored 20 for the Celtics, whose 11-game losing streak is their longest since dropping a franchise-worst 13 in a row during the 1996-97 season.
"At some point, we're going to win a game," Celtics coach Doc Rivers said. "Losing has to bother you enough that you get so (angry) that you do something about it. I understand they've got talent and all that stuff. But at some point, we have to demonstrate it."
Wally Szczerbiak returned from a nine-game absence with a sprained right ankle, and had nine points in a reserved role for Boston.
His 21-foot jumper with 3:24 left in the first quarter gave the Celtics their largest lead of the game at 27-22, but Arenas and Jamison scored all of Washington's points during an 8-0 run that gave the Wizards a 30-27 lead.
West pulled Boston to within 30-29 with a jumper in the closing seconds of the first quarter, and neither team was able to distance itself in the second quarter.
"It was good to be back out there and compete and play with my teammates," Szczerbiak said. "Unfortunately, they took the game over in the second half and we couldn't figure out a way to break this losing streak."
Boston center Kendrick Perkins set a season high with four assists. He surpassed his previous high of two in the first four minutes. ... Szczerbiak has missed 18 games this season with various injuries. ... Washington outrebounded Boston 51-38. ... The Celtics shot 57 percent in the first quarter, but finished at 39 percent.