World number one Rory McIlroy and 14-time major champion Tiger Woods fell in the first round of the World Golf Championships Match Play Championship on Thursday.
Ireland's Shane Lowry, ranked 68th in the world and the 64th-seed in the 64-man field, toppled Northern Ireland's McIlroy 1-up, while Charles Howell defeated Woods 2 and 1 at the Ritz Carlton Golf Club course at Dove Mountain.
Lowry, a friend of McIlroy's from their days in the amateur ranks, made his run on the back nine, chipping in for birdie to win the 12th hole and winning the 13th with an eagle to gain a two-up advantage.
McIlroy pulled one back at 14, but conceded the 15th after finding a series of bunkers. McIlroy then birdied the par-three 16th for a win, but they halved the last two holes with pars, and Lowry emerged victorious.
"Obviously it was always going to be a tough match for me against Rory today, but playing against the world number one, I'm feeling quite good now," said Lowry, who sank a four-foot par putt at 18 to seal the win.
"But it's important not to get too high now, because it's only the first round, and I've got another match tomorrow and am really looking forward to playing that."
Neither Howell nor Woods made a bogey in their match, which ended with darkness closing in.
"I knew I had to play my best to have a chance out there," Howell said, adding that his mind-set throughout was that he had "nothing to lose".
Woods, winner of this event in 2003, 2004 and 2008, has now failed to get out of the first round three times in his career, but said he couldn't complain about his game.
"We both played well," Woods said. "He made a couple of more birdies than I did. He played well and he's advancing."
The round was continued from Wednesday, when a freak snowstorm in the Arizona desert cut short play, and Thursday's start was delayed for several hours.
Two matches were halted by darkness. Sweden's Carl Pettersson was 1-up against Rickie Fowler through 17 holes with the winner to face Lowry.
Gonzalo Fernandez-Castano and Francesco Molinari were all-square through 15, with the winner to face Howell.
McIlroy, who missed the cut in his only other start of the year, the European Tour's Abu Dhabi HSBC Golf Championship, is under extra scrutiny in the wake of his switch to Nike equipment.
He said some ragged iron play cost him the match.
"I drove the ball really well," McIlroy said, but "couldn't take advantage of that."
World number three Luke Donald, who won the title in 2011 to launch a stellar year that saw him gain the world number one spot and win the European and US money titles, advanced with a 1-up victory over Germany's Marcel Siem.
South African Louis Oosthuizen, the fourth overall seed and top of his quarter, defeated Scotland's Richie Ramsay 2 and 1.