Needing a birdie on the par-4 18th for a 59, Watney drove into the left rough, failed to reach the green with his approach and left his long birdie pitch just short of the putting surface.
The American finished at 22-under 262 and earned $1.3 million in the unofficial PGA Tour event, finishing a stroke ahead of 2011 champion Bo Van Pelt and Robert Garrigus and three ahead of Tiger Woods.
The tournament will become a full-fledged PGA Tour event next year when the tour begins its new season in October after the FedEx Cup.
Needing a birdie on 18 to force a playoff, Van Pelt saved par after hitting into a greenside bunker. On Saturday, needing a closing birdie for a 59, he made a double bogey for a 62.
The players were allowed to lift, clean and place their golf balls in the fairways for the last three rounds because the course was soaked by tropical overnight storms.
Hanson finished at 21-under 267 on The Masters Course at Lake Malaren and earned $1,166,600 in the European Tour’s richest regular event. He won the KLM Open last month in the Netherlands and has six career tour victories.
The top-ranked McIlroy, the winner last year when the event was a non-sanctioned exhibition tournament, finished with a 67.
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