The clutch trey gave Bosh 23 points for the game, and the Heat forward also hauled down nine rebounds as Miami notched its 29th win in 30 games despite the absence of all-stars LeBron James and Dwyane Wade.
Heat Coach Erik Spoelstra elected to rest the pair for the contest with the Western Conference-leading Spurs, despite its implications for home-court advantage throughout the NBA playoffs.
James was tending to a nagging right hamstring strain while Wade was resting an ailing right ankle.
San Antonio was fined $250,000 by the NBA for that move.
Duncan and Kawhi Leonard combined for 34 points and 23 rebounds for the Spurs.