Rory McIlroy fired a closing round of one-over-par 72 to end on seven under at the Deutsche Bank Championship.
Graeme McDowell shot a 70, including two birdies and one bogey, to join McIlroy in a tie for 47th position.
That left the Northern Irishmen 15 shots behind the winner, Sweden's Henrik Stenson, who finished two shots ahead of American Steve Stricker.
McIlroy's round was marred by two double bogeys and a bogey but he also posted four birdies.
The 24-year-old defending champion had shown a return to form by signing for an impressive 64 in his third round in Boston.
Play in Monday's final round was delayed by 90 minutes because of an electrical storm and McIlroy began his round poorly with a double bogey sixth at the 10th.
After hitting his approach into deep rough a few yards to the left of the green, the world number four took three more strokes to get onto the putting surface.
Further misery followed at 14, where he made six after thinning his escape from a right greenside trap 20 yards through the green.
Both McIlroy and McDowell have qualified for the third FedEx Cup play-off.
Stenson chipped in at the 17th hole to register a record score for the tournament as he saw off the challenge of Stricker.