The Cavaliers had five players in double figures including Thomas who showed flashes of his offensive skill in a long-awaited first game with his fourth National Basketball Association team.
Thomas tallied 17 points in 19 minutes of play as he embarks on a soft return to NBA action following injuries to his hip and shoulder.
"It was great see him get his first basket and go from there," James said of Thomas. "He is a spark and the jump we needed on our team right now."
Thomas and Dwyane Wade came off the bench to score 16 and 15 points respectively.
Thomas' last game was May 19, game two of the Eastern Conference finals against the Cavs. He played hurt through the first two rounds of the playoffs, then was furious that Boston traded him.
Cavaliers coach Tyronn Lue said earlier that Thomas would play restricted minutes on Tuesday. Even though the Cavaliers' next game is against the Celtics, Thomas already said he isn't keen on facing his old teammates just yet.
"I can wait until February," Thomas said when announcing his return. "I think we play them in February again, so I can wait and put on a show then."
Damian Lillard returned to the Blazers lineup from injury and finished with 22 points. Lillard missed five games with a sore right hamstring.
Jusuf Nurkic scored a team-high 23 points and CJ McCollum chipped in 19 in the loss.