The South Korean, who hasn't won on the US tour since he beat Tiger Woods at
the 2009 PGA Championship, said a couple of mistakes early in the round helped
him get focused for the back nine on the Stadium Course at TPC Scottsdale.
Leading first-round scores on Thursday in the $6.2m PGA Tour's Phoenix Open (USA unless noted, par-71):
64 - YE Yang (KOR), Bubba Watson
65 - Pat Perez, Kevin Stadler, William McGirt, Greg Chalmers (AUS), Matt Jones, Harris English, Chris Kirk
66 - Hunter Mahan, Keegan Bradley, Ryan Moore, Tommy Gainey, Jason Kokrak, Brendon de Jonge (ZIM), Brendan Steele, Hideki Matsuyama (JPN)
67 - Bryce Molder, James Driscoll, Sang-Moon Bae (KOR), Martin Laird (GBR), Erik Compton, Spencer Levin, Michael Putnam, John Mallinger, Graham DeLaet (CAN), Lee Westwood (GBR), Patrick Reed, Gary Woodland, Scott Piercy