The third-year pro followed up a missed left corner three-pointer by Patty Mills with the two-handed slam. No one on the Heat boxed him out as he crashed the paint from the top of the key and completed the dunk cleanly.
The dunk gave the Spurs a 55-33 lead, and San Antonio went into the break leading 55-36.
The Spurs entered Thursday holding a 2-1 series lead over the Heat as they seek to avenge their loss in the 2013 Finals.
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