Ten players were unable to complete the opening round before action was called due to darkness.
Yang, who held off Tiger Woods to win the 2009 PGA Championship, shot a 30 on the back nine of the TPC-Scottsdale course. Watson, winner of the 2012 Masters, birdied four out of five holes beginning at the par-5 13th.
Phil Mickelson, the defending champion whose appearance this week was questionable all the way up to his morning tee time Thursday, shot an even-par 71. Mickelson suffered lower back pain last week and withdrew after the second round of the Farmers Insurance Open.
Patrick Reed, who did not play last week after capturing the Humana Challenge the week before, shot a 67. In winning the second event of his career, Reed became the first player in PGA Tour history to shoot 63 in each of the first three rounds.