Greg Chalmers parred the seventh hole of a playoff while
Chalmers, who shot 64 Sunday after trailing the leaders by seven strokes going into the final round, and Scott and Wade Ormsby, who both shot 71, finished with 72-hole totals of 11-under 277.
Ormsby dropped out of the playoff when he parred the third playoff hole at Royal Pines in Gold Coast, Australia, while Chalmers and Scott made birdie.
Scott missed a 12-foot birdie putt on the first playoff hole that would have won it, and did the same on the second extra hole, when Ormsby missed from seven feet.
The 2011 champion was in a three-way lead with Fraser and Kaymer on 8 under with two holes to go but the German bogeyed the 17th while the Australian missed an easy par putt on the 18th, giving Westwood, who was watching in the clubhouse, the victory.
Westwood came back from two straight bogeys at the start of his final round to fire seven birdies for a 67 and an 8-under 280 total.
Branden Grace held his nerve on the final day to win the Alfred Dunhill Championship by seven shots at Leopard Creek Country Club in Malelane, South Africa.
The South African started the day with a one-shot advantage over Lucas Bjerregaard, but quickly gained breathing space when the Dane had a bogey on the first and Grace birdied the second.
Bjerregaard fell away badly thereafter to card a 17-over 89, while Grace went on to record a 4-under 68 and finish with a 20-under 268 for the event.