Duncan led the Spurs with 26 points on 11-of-16 shooting and had 11 rebounds to help extend San Antonio's winning streak to five games.
Kawhi Leonard chipped in 14 points and Manu Ginobili had 13 plus five assists.
San Antonio led 88-87 at the end of three quarters and then went off on a 13-2 run in the fourth quarter to put the game out of reach.
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