MARANA, Arizona (Reuters) - Ireland's Shane Lowry knew "deep down" that he could beat Rory McIlroy and drew on that self-belief to pull off a stunning upset over the world number one in the snow-delayed first round of the WGC-Accenture Match Play Championship on Thursday.
Ranked 68th in the world, Lowry chipped in twice for birdie after the turn to take control against his good friend before getting up and down from a greenside bunker to par the 18th and seal victory in fading light at Dove Mountain.
"I'm very happy to be honest," Lowry told reporters. "Obviously it was always going to be a tough match for me against Rory today, playing against the world number one. I'm feeling quite good now.
"Deep down I knew I could beat him. I'm not here for no reason. I'm not here to make up the numbers.
"But it's important not to get too high now because it's only the first round. I've got another match tomorrow and I'm really looking forward to playing that."
The 25-year-old Lowry will next meet either Swede Carl Pettersson or American Rickie Fowler, who will have to complete their first-round match early on Friday. Pettersson was one up after 17 holes.
"I didn't make enough birdies in the end," said the 23-year-old McIlroy. "Shane had a nice little stretch around part of the back nine. I hung in there, but I just didn't do enough.
"I probably would have lost by more if I had played someone else in the field. It wasn't a great quality match. I missed a lot of irons right."
Lowry, who has known twice major winner McIlroy since their amateur days, made a stumbling start, bogeys at the second, third and fourth leaving him two down.
Beaten in last year's final by American Hunter Mahan, McIlroy bogeyed the par-three sixth after missing the green well to the right for his lead to be trimmed to one and Lowry birdied the seventh to make it all square.
Though Lowry also faltered with another bogey at the ninth, he then took control in explosive fashion.
He chipped in from 18 feet to birdie the par-five 11th and holed out from double that distance from behind the green for another birdie at the par-three 12th, to go 1 up.
A stunning three-wood from Lowry at the par-five 13th, where his ball eventually settled just three feet from the flag, led to a conceded eagle there after McIlroy missed a birdie attempt from just five feet.
Lowry slipped up with a three-putt bogey at the par-four 14th but he got back to two up after the world number one made a hash of the 15th.
McIlroy's drive ended up next to a bush well left of the green from where he played left-handed, dumping his ball into a greenside bunker. With daylight fading, McIlroy bladed his third shot over the back of the green and conceded the hole.
McIlroy again pulled one back when he rolled in a nine-footer to birdie the short 16th but Lowry hung on with matching pars at 17 and 18 to wrap up the win.
"I was quite nervous starting off," said Lowry, who became only the third amateur to triumph on the European Tour with a playoff victory for the 2009 Irish Open.
"I handed him a few holes early doors, but he handed me a few back later on in the round. And this is match play, and I got a few breaks where I needed them, and I'm just fortunate to win."
Reporting by Mark Lamport-Stokes; Editing by Peter Rutherford/greg Stutchbury