BOSTON -- The Boston Celtics know any road to the NBA Finals will likely pass through Cleveland.
They put the defending champs on notice that they are gearing up to challenge them for their Eastern Conference throne.
Boston's win overshadowed the seventh triple-double of the season for James, who finished with 28 points, 13 rebounds and 10 assists. Kyrie Irving added 28 points for the Cavaliers, who lost for the first time when leading at any point in the fourth quarter on the road.
The game marked the third meeting this season between the top two teams in the East, and the first win by the Celtics.
"We just played to win," Thomas said. "They're the No. 1 team in the East. One of the best teams in the NBA, and we just wanted to protect home court and get a win. We did that tonight."
Jae Crowder had 17 points and 10 rebounds for Boston, which led by three entering the fourth quarter before there were six ties and 10 lead changes in the final 12 minutes.
It was a 3-point barrage down the stretch, with the Celtics connecting on six straight attempts during one stretch. They also made this more difficult for a Cavs team that had averaged 126 points in its wins over the Celtics.
"This needs to carry over for us," Celtics guard Avery Bradley said.
Deron Williams, signed by Cleveland earlier this week, scored four points in 24 minutes in his Cavaliers debut. But it did little to help the Cavs overcome a night in which they were outrebounded 47-41.
It was tied at 99 when Thomas connected on a pair of free throws to put Boston in front 101-99. Irving then missed a jumper and Tristan Thompson grabbed the rebound and got it to Deron Williams, who then missed from the corner. Crowder got the rebound, was fouled and made his two foul shots to seal it.
"I saw Crowder running to me, he jumped and then I saw Marcus Smart running toward me," James said of the Cavs' missed opportunity in the waning seconds. "I saw D-Will naked in the corner, so I gave him an opportunity and he just missed it. We got the shot we wanted."
Despite the loss, coach Tyronn Lue was pleased with his team's effort.
"It was a good game -- went down to the wire, shot for shot," Lue said. "I.T. made two big shots, Avery made two big shots. We competed, we fought. That's all you can ask for."
Cavaliers: Outscored the Celtics 50-42 in the paint. ... Finished 15 of 22 from the free-throw line.
Celtics: Al Horford finished with nine points, 10 rebounds and 10 assists. ... Finished 13 of 31 from the 3-point line.
"I don't know if I'm in his level. I definitely slowed up because I knew it was him. I'm not taking no legend out." -- James on his near collision with Patriots coach Bill Belichick, who was seated on the baseline.
Celtics coach Brad Stevens said he's been impressed by the recent additions by several teams in the Eastern Conference. Though, he said, the line still forms behind the defending champions following their acquisition of Williams and anticipated addition of big man Andrew Bogut, who is free to sign after clearing waivers.
"I don't think I'm saying anything earth-shattering here: We're all chasing Cleveland," Stevens said.
Derrick Williams -- playing on his second 10-day contract -- provided the energy for the Cavaliers early on, scoring 10 points in the first half.
He scored from the outside, got into the teeth of Boston's interior defense and sped the game up. One of his best highlights came in the second quarter when he blocked Bradley's jumper, sprinted ahead and received a pass from James for a fast-break dunk.
Cavaliers: Continue their three-game road trip Friday at Atlanta.
Celtics: Have two days before beginning a five-game road trip Friday against the Lakers.
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