(Reuters) - William McGirt, relying on his putter, held his nerve in blustery conditions to clinch his maiden PGA Tour title with a playoff victory over fellow American Jon Curran at the Memorial tournament in Dublin, Ohio, on Sunday.

The 36-year-old journeyman sealed the win with a superb up-and-down for par on the second extra hole, the challenging 18th at Muirfield Village, after both players had parred the same hole at the first attempt.

After overshooting the green with his approach, McGirt hit a brilliant flop shot six feet past the cup and coolly sank the putt after Curran, also over the back of the green in two, failed to save par.

The duo had finished the 72 regulation holes at 15-under-par 273, McGirt carding a flawless one-under 71 while Curran closed with a four-birdie 70 in a final round interrupted for nearly 90 minutes due to the threat of lightning.

"It's unbelievable," McGirt told CBS Sports after earning the winner's check for $1.53 million, a coveted spot in next year's Masters and congratulations from tournament host Jack Nicklaus as he walked off the 18th green.

"It was a struggle all day. I fought my golf swing all day but I just tried to hold on to it and just hit as many greens as I could. Made a lot of really good par putts.

"My putter really saved me this week."

Though McGirt carded just one birdie on the day, he did not drop a single shot as he finally claimed his maiden PGA Tour title in his 165th career start.

Long-hitting Dustin Johnson, the first-round leader, returned a 71 to finish third at 14 under, one stroke better than fellow Americans Matt Kuchar (73), Gary Woodland (73) and J.B. Holmes (69), and Northern Ireland's Rory McIlroy (68).

Kuchar, the 2013 champion and one of three players tied for the lead overnight, had moved one stroke clear after reaching the turn in two-under but struggled early on the back nine with bogeys on 12 and 15 and a double on 13.

"It was challenging," said Kuchar, who did well to cover the last three holes in one-under. "I came out on the front nine, I played great, great golf. I mean, I really, really was in full control. And then a couple of less than great shots."

Australian world number one Jason Day, who landed his third PGA Tour victory of the season at the Players Championship last month, finished six shots off the pace with a roller-coaster 74 after starting the final round three off the lead.

"Today was just all over the shop ... missing greens with wedges in the hand," said Day, whose round included a double-bogey at the 12th, five birdies and five bogeys.

"Just wasn't as sharp as I would have liked to have been. It is what it is. You can't win them all."

(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Larry Fine)