Haas also won the $10 million prize for finishing first in the race for the FedExCup.
The duo matched pars on the first two playoff holes.
On No. 18, the third extra hole, Haas two-putted from the fringe from 48 feet out for the win. Mahan found a bunker off the tee, and missed a 15-footer for par that would have extended the playoff session.
Haas closed with a two-under 69 and Mahan posted a one-over 71. They finished at eight-under-par 272.
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