The outcome was unexpected considering the Lakers' Kobe Bryant sat out his third straight game with a sore shin and because San Antonio had only four previous home losses this season.
San Antonio missed a chance to move into a tie with Oklahoma City for the top spot in the Western Conference.
Bynum also scored 16 points and Paul Gasol produced 21 points with 11 rebounds. Los Angeles won the battle of the boards 60-33 and has six victories in its last eight games.
After winning 11 in a row, the Spurs have dropped two straight.
Los Angeles took a 16-point lead into the fourth quarter after holding the Spurs to 16 in the third.
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