The trio all finished on 15-under-par at Muirfield Village, but it was overnight leader DeChambeau who held his nerve to claim his second PGA Tour title after a two-hole playoff.
DeChambeau looked to have thrown away the victory when he three-putted for a bogey on the 18th to finish the day on 71, taking him into the playoff after An had hit 69 and Stanley recorded a round of 70.
The 24-year-old American then missed the fairway on the 18th during the first extra hole but managed to match An's score, while compatriot Stanley was eliminated with a bogey.
However, DeChambeau got it right at the third time of asking when he holed a 12-foot birdie putt to take the title on the second extra hole, narrowly beating An.
Tiger Woods had also left himself in contention going into the final day, but the five-time champion shot an even 72 to leave himself tied in 23rd and six shots off the pace.
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