The Celtics are now 0-4 in Cleveland overall this season and will have to return for Game 6 Friday.
"We'll get the next one," said Paul Pierce, who had 13 points on 6-of-17 shooting. "I feel like, hey, every time we get a chance to step on the court, we have an opportunity to win.
"We're definitely not discouraged with the loss, especially on the road. Hopefully, we can play better at home and break this road streak so everyone can stop talking about it."
This season, the Celtics had an NBA-best 31 road wins. But they haven't won a road game since April 14 at New York. However, they are 6-0 in the postseason at TD Banknorth Garden and 4-0 overall there against Cleveland.
"The win was, of course, big," said Cavaliers forward LeBron James, who had 21 points, 13 assists, 6 rebounds, 3 steals, and 2 blocks. "We took care of home court. That's what we needed to do and we made it a three-game series."
The Celtics were outscored, 20-12, in the fourth quarter - their lowest-scoring quarter of the postseason. In the period, they shot 31.3 percent from the field and had zero offensive rebounds.
The individual scoring for Boston in the fourth consisted of 6 points from Paul Pierce, 4 from P.J. Brown, and 2 from Sam Cassell. Kevin Garnett and Ray Allen both scored 15 for the game but went scoreless in the fourth. Cleveland also nailed three 3-pointers in the fourth.
"It's pretty frustrating," Garnett said. "We put ourselves in a pretty good position to win the game. Obviously, we didn't have the fourth quarter we normally have."
Coach Doc Rivers said his team needed to play better "under stress" during the final stretch of games. Pierce and Garnett begged to differ.
"I wouldn't say we're lacking poise," Garnett said. "In a situation like ours, we are trying to do everything that Doc wants us to do. He makes all the calls. He gives us direction. For the most part, we pretty much try to do what he wants."
Said Pierce, "I don't know what he means. I'm stressed every game. Stressed to get a win."
No Boston player scored more than 15 points, and as a team, the Celtics shot 38.6 percent from the field, including 3 for 14 on 3-pointers. They had only 2 fast-break points and 5 second-chance points.
"Defensively, what we've been doing is excellent," James said.