Boston can now advance to meet the Cleveland Cavaliers in the next round with a victory Friday in Washington.
Avery Bradley tallied a postseason career high 29 points in the blowout as Boston can now advance to meet the Cleveland Cavaliers in the next round with a victory Friday in Washington.
"Everyone was prepared," said Bradley. "And that's what it's all about."
The Celtics and Wizards have played nine times this year, and the home team has won all nine games. Boston has now won eight straight overall at the Boston Garden over Washington.
The Celtics got on an early 16-0 run and never looked back. Their first quarter burst came after the Wizards scored the first four points of the game.
Bradley, who is playing with a sore hip, scored 25 points in the first half as the Celtics compiled a 22-point halftime lead.
"He put his injuries aside and laced his shoes up and played," teammate Isaiah Thomas said of Bradley. "He was the key to this game at both ends of the floor."
Bradley hit his last basket with 5:55 left in the third quarter and rested in the fourth.
Al Horford finished with 19 points and added seven assists and six rebounds for Boston.
Thomas and Jae Crowder both scored 18, Thomas with nine assists and Crowder with eight rebounds. Thomas scored eight consecutive points in the fourth with Bradley on the bench.
Thomas said the coaching staff did a good job of getting them ready for game five.
"We just wanted to impose our will," said Thomas. "The coaches kept saying that, 'Impose your will.' We were the more physical team tonight.
"We took what was on the whiteboard and we put it on the court,"
The Celtics went 16-for-33 from beyond the arc and became the sixth team in NBA history with at least 10 three pointers in six straight postseason.
John Wall led the Wizards with 21 points, and Bradley Beal had 16 and Otto Porter added 13.
The Wizard guards combined to go just 14 of 36 from the floor, two of seven from three-point range.
"When you give a very good team transition points and breakaway points with nobody guarding you ... it's going to be hard to keep up with them," Washington coach Scott Brooks said. "We had no answers for those guys. We've done a pretty good job on their best player, but not (a) good enough job on the other guys."
If the Celtics win Friday, they would open against Cleveland on Monday. If the Boston-Washington series goes seven games, the winner meets the Cavaliers next Wednesday.