James was one of four players with more than 20 points for the Central Division-leading Cavaliers, who have won 12 of their last 13 games against Western Conference opponents and broke a 14-game losing streak in Texas.
Kyrie Irving scored 22 points, while Kevin Love had 21 points and 14 rebounds. J.R. Smith also scored 21 points and Timofey Mozgov, the other starter, had 17.
Chandler Parsons led Dallas with 18 points, while Monta Ellis had 17 and Amare Stoudemire 15. Dirk Nowitzki scored 13 points on only 3-of-10 shooting.
James first took off his headband in the second quarter of Cleveland's home game Saturday and never put it back on against Phoenix, saying afterward, "It just happened."
While James never slipped on a headband against the Mavericks, No. 23 was still easily recognized by how he played. He finished 10-of-14 shooting with seven rebounds and eight assists.
Dallas started the second quarter with a 31-26 lead, but James hit consecutive 3-pointers and then took the Cavs' assist record all to himself with a pass to James Jones for another 3-pointer that made it 35-all less than 2 minutes into the quarter.
That was James' first assist of the game and his 4,207th in a Cleveland uniform, breaking a tie with Mark Price for the franchise record.
The trio of 3s started a 41-point second quarter for Cleveland, which led for good after Iman Shumpert had a steal and passed ahead to James for a fast-break layup that made it 39-38. The Cavs led 67-53 by halftime.
Back in Cleveland after four seasons with the Miami Heat, James was already the Cavaliers' career leader for points, field goals made and attempted, 3-pointers made and attempted, free throws made and attempted, steals and minutes played. He played his first seven NBA seasons with the Cavs.
Cavaliers: Tristan Thompson played in his 272nd consecutive regular-season game, the NBA's second-longest active streak behind the 304 in a row by DeAndre Jordan of the Los Angeles Clippers. ... Anderson Varejao, out for the season with a torn Achilles, posted video of himself shooting flat-footed shots earlier Tuesday. Coach David Blatt said Varejao's recovery is "protocol-oriented" and will be step by step. "Andy will try to push the envelope," Blatt said. "Since he's not coming back this year, we will not allow him to."
Mavericks: Al-Farouq Aminu, who was defending James early in the game, didn't play in the second half after taking a hard hit to the left shoulder in a collision with Smith before halftime. ... Only one other time this season did Dallas allow more points in the first half. Phoenix scored 69 points on Dec. 5. ... Devin Harris returned after missing two games with a right hand injury.
Cavaliers: At San Antonio on Thursday night.
Mavericks: Host the Los Angeles Clippers on Friday night.