Ireland's Darren Clarke is tied for third after firing a bogey-free nine-under-par 63 on day one of the Las Vegas Invitational.
The 35-year-old began on the back nine and fired five birdies before the turn. He then added another four to lie one shot off the lead.
Stuart Appleby finished on 10-under-par 62 with six straight birdies, and Steve Flesch started the day with five consecutive birdies to match the Australian's score.
Both players burnt up the Southern Highlands Golf Club, one of three courses used in the 90-hole pro-am - the others being the host TPC at Summerlin, where Clarke played, and TPC at The Canyons.
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Dan Forsman and Craig Barlow also fired 62s but their scores were on the par-71 Canyons course.