Tied for the lead at 14 under and playing several groups ahead of the final group, Thomas had 111 metres to the flag for his second shot on the par-four closing hole and knocked it in for an eagle with what looked like a winning shot.
It capped a stunning 62-64 weekend total for the 24-year-old but his hopes of victory were quashed by Phil Mickelson who eventually defeated Thomas in a playoff.
The victory is Mickelson's first anywhere since the 2013 Open Championship.
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