Mills, finishing his first season with the Spurs after spending two years with Portland, scored 34 points and had 12 assists. In San Antonio's previous game he had scored 27 points against Phoenix.
San Antonio's top regulars sat out the regular-season closer, just as they have on several occasions this season while Coach Gregg Popovich attempted to save his stars for the playoffs.
Nevertheless, the Spurs reached 50 wins for the season and tied Chicago for the best record in the NBA. Chicago won its only meeting with San Antonio and thus earned the No. 1 seed for the playoffs.
San Antonio's playoff campaign will begin Sunday against Utah.
Chris Wright scored 25 points for the Warriors, who won just once in their final 11 games.
The contest between San Antonio and Golden State was the last of the 990 regular-season games in the lockout-shortened NBA season. A regular campaign consists of 1,230 games.