It was the Suns' only lead of the fourth quarter.
Duncan, who had 24 points and 11 rebounds, missed an off-balance 5m shot at the buzzer.
The victory tied the best-of-seven first-round series at 2-2, with Game 5 Tuesday in San Antonio.
Stephon Marbury scored 18 points, Shawn Marion had 17 points and Hardaway had 13 points and seven assists, including the game-winner.
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