Graeme McDowell slipped further down the leaderboard in the final round of The Heritage event in South Carolina after a second successive round of 74.
The Portrush player went out in a three-over 39 despite an early birdie.
McDowell's round stuttered with two bogeys and a double-bogey at the par-three seventh and he then completed the back nine in a level-par 36.
McDowell's best showing on the PGA Tour this year is his second place at the Tournament of Champions in January.
England's Luke Donald narrowly missed the chance to become world number one after losing a sudden-death play-off to Brandt Snedeker at The Heritage.
The result means Englishman Lee Westwood reclaims the number one spot after winning the Indonesia Masters.
Both players finished the tournament on 12 under par but Snedeker snatched victory at the third play-off hole when Donald's chip lipped out at the 18th.
Snedeker had fired a seven-under-par 64, while Donald could only make a 70.