Palmer earned his third PGA Tour title at the 2010 Sony Open. He missed the cut at this event last year.
Webb Simpson, a two-time winner last year, carded a six-under 65 and is alone in second place. Harrison Frazar, Kevin Na, Chez Reavie, Derek Lamely and Jarrod Lyle are tied for third after posting five-under 66s.
The start of the first round at TPC Scottsdale was delayed one hour by frost. The round was suspended by darkness at 8:05 p.m. (et) and will resume Friday 9:30 a.m. The second round will start as scheduled at 9:30 a.m.
MORE TO FOLLOW.