O'Malley finished regulation at 14-under-par 274 along with fellow Australian Steven Bowditch, who fired a 63 in the final round to force the extra session. O'Malley was leading at 15 under with one hole to play, but a bogey at the 18th left him with a round of 69 and he was headed to a playoff.
The duo parred the first three playoff holes and returned to the 18th tee to play a fourth extra hole. Both players found the fairway off the tee and O'Malley knocked his approach within 25 feet of the cup. Bowditch was less fortunate with his second shot and left himself with a lengthy putt for birdie.
Bowditch ran his putt past the hole while O'Malley calmly converted his birdie try for the win.
O'Malley was part of a three-way tie for the lead heading into the final round at Clearwater Golf Club and the veteran pushed ahead with two consecutive birdies starting at the par-5 second. He struggled to a bogey at the fourth but recovered with a birdie at the sixth.
The 39-year-old picked up another birdie at the 10th and made it two in a row with a birdie at the par-3 11th. O'Malley bogeyed the 12th but got back to minus-15 with a birdie at the 15th and was in control until the late bogey delayed his victory.
'As it turned out, it was a very rewarding day,' said O'Malley. 'I played really well this week and it would have been a shame to play that well and not come away with the trophy.'
Bowditch, who won the Jacob's Creek Open, was hurt by a 76 in the third round, but he came out firing on Sunday with five birdies over his first nine holes. Bowditch reached 11 under with a birdie at the 10th and surged to the top of the leaderboard with three straight birdies from the 12th. He then parred his remaining holes to match the course record.
Johnson Wagner and Jerry Smith tied for third at 11-under-par 277. Brandt Snedeker, Steven Jeffress and Troy Matteson shared fifth place at 10-under-par 278.