Louis Oosthuizen and Watson finished regulation tied at 10-under. On the first hole of the playoff, No. 18, Oosthuizen narrowly missed his 15-foot birdie putt, opening the door for Watson. The former University of Georgia golfer missed his eight-foot birdie attempt.
On the second playoff hole, Watson hooked his tee shot deep into the woods at No. 10, while Oosthuizen also went into the right fringe. Oosthuizen hit his approach in front of the green. Watson hooked a wedge around the trees from 155 yards to the middle of the green.
Oosthuizen chipped long to the back of the green and missed his par attempt. Watson two-putted from 12 feet for the victory.
The long-hitting Watson bogeyed the par-3 12th to fall two back. He responded with a four-hole stretch of birdies starting at No. 13. Watson rolled in a six-foot birdie putt at No. 16 to tie Oosthuizen for the lead.
Oosthuizen recorded a rare double eagle at the par-5 second hole. He birdied Nos. 13 and 15 to move to 10-under.
Watson and Oosthuizen each made par at No. 17. At No. 18, Oosthuizen hit his approach to the back of the green, while Watson left himself a 25-foot birdie attempt to the right. Both players missed their birdie attempts and will now face each other in a sudden-death playoff that begins on No. 18.
Matt Kuchar eagled No. 15 to briefly tie Oosthuizen for the lead. Kuchar then missed the green at No. 16 and made bogey. He finished with 69 to tie for third at 8-under with Lee Westwood (68), Peter Hanson (73) and Phil Mickelson (72).
Mickelson sliced his tee shot into the trees at the par-3 fourth. He took two shots to get out and eventually made triple bogey.
Hanson, the third-round leader, bogeyed Nos. 1 and 3 and played catch-up all day.
Bo Van Pelt shot the round of the day with 64. He made one of two holes-in-one at No. 16, along with Adam Scott, who shot 66 and climbed into a tie for eighth.
Van Pelt just missed finishing in the top 16, which automatically qualifies golfers for the 2013 Masters. Van Pelt finished tied for 17th place.