McIlroy led Koepka by a stroke going into the ultimate spherical however as a substitute of an epic duel with the world No.1 he faltered with a 71 because the American surged previous with a 65 to win the WGC-FedEx St Jude Invitational by three from countryman American Webb Simpson.
The 30-year-old McIlroy, who had gone clear after a blistering 62 Saturday, resulted in a tie for fourth, 5 strokes adrift.
The four-time main winner has climbed again as much as world No.three in a strong season by which he has received the Gamers Championship and the Canadian Open however he has additionally has failed to interrupt 70 seven instances in his 13 PGA Tour last rounds this season.
The highly effective Floridian, who has received 4 of his final 10 majors, pulled alongside McIlroy with a birdie on the third after which took management with birdies on the fifth and sixth as his enjoying accomplice misplaced floor.
“It is unbelievable. To take a look at what I’ve performed this yr, simply present consistency, attempt to take my recreation to a brand new stage and I’ve performed that,” Koepka stated, who leads the season-long FedEx Cup standings.
“To win this title in opposition to Rory was fairly particular.”