Nowitzki was kicked when he was fouled with 3:10 left in the third quarter. He left the game 17 seconds later and the training staff wrapped his thumb on the bench.
Nowitzki returned with 8:01 remaining in the game and was fouled hard driving to the basket seconds later.
"I bruised it two games ago and I got it kicked tonight," Nowitzki said. "So it'll stay sore for a while. But I was able to tape it and stay out there."
Nowitzki scored nine of his 20 points in the final stanza, helping the Mavs overcome a season-high 46 points from Warriors guard Monta Ellis.
Information from the Associated Press was used in this report