Thomas finished with 22 points and already looks like a better fit in coach Luke Walton’s offense than he did in an ill-fated 15-game stint with Cleveland after the offseason trade that sent Kyrie Irving to Boston.
The diminutive guard’s first half with the Lakers was his highest-scoring half of the season, a team-high 16 points.
Thomas, who was part of a four-player deal at the trading deadline that also brought Channing Frye, missed the first 36 games recovering from a hip injury.
Doug McDermott had eight points in his Dallas debut following a deadline deal that brought him from New York and was part of a youthful closing lineup that outscored the Lakers 13-5 in the final 3:09.
The Lakers had a season-best, four-game winning streak stopped for the third time in a month.
Nowitzki, Barnes and starting guard Wesley Matthews all sat in the last three minutes, and rookie guard Dennis Smith Jr. put Dallas ahead for good at 119-118 on a layup. Smith finished with 14 points, and the Mavericks had a season high in points.
Julius Randle had 26 points, eight rebounds and seven assists for the Lakers, and Brandon Ingram scored 22 points. Kyle Kuzma had 12 points and 15 rebounds.
Dwight Powell scored 19, two shy of his career high, for Dallas. J.J. Barea had 10 points and nine assists.
Thomas entered the game to a noticeable ovation from the usually solid number of Lakers fans in the Dallas crowd, and hit a 3 from the left wing on his first LA possession in what proved to be just a start. He was 4 of 7 from long range before halftime.
