Cleveland won for the fifth time in six games and has beaten the Celtics seven straight times. James scored only four points in the fourth quarter but has averaged 35 points during the Cavaliers' winning streak against Boston.
"The difference between this year's team and last year's team is we could sneak up on people last year," James said. "We aren't surprising anybody this year and teams are always ready to play us."
After Ilgauskas put the Cavaliers ahead 105-101 with 43 seconds remaining, Wally Szczerbiak hit a pair of free throws and Tony Allen made one to cut Cleveland's lead to 105-104. Allen then fouled James with 7.6 seconds left on the inbounds and he drained a pair of free throws before Szczerbiak missed a 3-pointer at the buzzer.
"The guys look to me to knock down those shots and I wasn't able to do it tonight," Szczerbiak said.
Cleveland won for the second time in its last seven road games and tied Orlando and Chicago for most wins in the Eastern Conference with 19.
Allen scored 22 points and Al Jefferson added 18 points and 12 rebounds for Boston, which has won once in the last eight games.
"The losing gets to everybody," Allen said. "A loss hurts. We just have to look at the film and see how to correct it."
James connected on an 80-foot heave as time expired in the third quarter to give Cleveland an 82-76 lead. James had 14 in the period and the Cavaliers closed the quarter with a 12-1 run.
"The two free throws at the end of the game were bigger than the long three," James said. "It made them shoot a contested 3-pointer at the end of the game."
Reserve Gerald Green had 21 points, including 14 in the second quarter for Boston, which fell to 4-11 at home.
Ilgauskas led Cleveland and Jefferson paced Boston with 11 points while the teams combined for 13 turnovers in the first quarter. James capped an 8-0 run with a 10-foot jumper to pull the Cavaliers to 45-43 with 2:58 remaining in the first half. The Celtics were ahead 54-49 at the break.
"He (Ilgauskas) is capable of a double-double every night," Cavaliers coach Mike Brown said. "He can score in the post, he passes well out of double-teams and offensively he has the whole package."
Drew Gooden added 13 and grabbed 12 rebounds for Cleveland.
- Cleveland's winning streak against Boston is its longest against any NBA team.
- Allen has led the Celtics in scoring in five of the last six games.
- Cleveland is 19-62 all-time in Boston.
- Paul Pierce's earliest return will be Jan. 19.
- Patriots linebacker Mike Vrabel and nose tackle Vince Wilfork attended the game.
- Boston shot 57 percent in the first half.