MARANA, Ariz. -- Luke Donald staved off the kind of upset bid that caught up with the world's No. 1 and 2 players late Thursday when he won the 18th hole to beat Marcel Siem.
Donald made six birdies, including a pair on the last two holes -- the first from 9 feet to halve the 17th and the second from 7 for the win. Three of those birdies had come on the front nine as the Englishman built a 2-up advantage.
But Siem, who was making his World Golf Championships-Accenture Match Play Championship debut, began to assert himself on the back nine. The pony-tailed German won the 10th hole with a chip-in birdie, the 11th when Donald bogeyed and the 12th with a 28-foot birdie putt to take his only lead of the day.
"I didn't worry because I was hitting good shots still," the Englishman said. "I hit a couple left shots on the back nine but drove it great today, hardly missed a fairway, hit a lot of solid iron shots and putted well. I obviously made it tough on him, too, and I just ... felt good about my game, so I wasn't worried when I went 1 down on 12."
Donald, who was the 2011 champion at Dove Mountain, answered with a 6-foot birdie putt at the par-5 13th to even the match. The next four holes were halved with a bogey, two pars and a birdie, before Donald converted at No. 18 for the win after Siem missed from 13 feet.
"I had to finish strong against Marcel," Donald said. "He pushed me all the way. He really played solid today. I threw six birdies in, but he had a couple chip-ins and holed some long putts and made it very difficult. It's always nice to get through that first round, and sometimes having a tough match is a good thing."
Donald faces Scott Piercy, a 4-and-3 winner over Paul Lawrie in his Accenture Match Play Championship debut, in Friday's second round.