San Antonio jumped into the third spot in the Western Conference and Houston dropped from third to sixth.
The Spurs had a four-point lead when Harden made a layup for his first points of the half with less than 90 seconds remaining.
Duncan missed a layup before Harden made a three-pointer with 28.9 seconds left to get Houston to 104-103.
But Duncan blocked Harden's shot and grabbed the rebound to secure the victory.
The close game ended a streak of nine straight wins by at least 12 points, which had tied an
Harden, who entered the game leading the NBA in scoring, had just 16 points as San Antonio Coach
at Atlanta 104, Charlotte 80:
at New Orleans 90, Phoenix 75:
Memphis 89, at Utah 88:
at Oklahoma City 116, Sacramento 103:
at Brooklyn 117, Washington 80:
Indiana 107, at Detroit 103:
Dallas 144, at Denver 143 (2OT):
Boston 99, at Cleveland 90: Marcus Smart scored 19 points, and the
Toronto 101, at Orlando 99:
Milwaukee 99, at New York 91: Giannis Antetokounmpo returned to the lineup with 23 points and moved the Bucks to the verge of a playoff spot with a victory over the