Ginobili blew past Ray Allen in transition to throw down the left-handed poster dunk over Bosh, who contested at the rim.
After trailing by seven points at the end of the first quarter, San Antonio went on a 33-13 run to re-take the lead.
The Spurs are seeking the fifth title of the Tim Duncan era. The Heat are hoping to become the first team to climb out of a 3-1 series deficit in Finals history.
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