Singh, a two-time defending champion, birdied four straight holes -- 13-16 -- to end up in second place at 8-under 64.
"I just played well today, and made some nice putts to get it going," Singh said. "Momentum is good, plus (the greens are) pretty soft so you can go for the flags."
World No. 1 Tiger Woods, the 2002 champion, shot 6-under 66, and shares sixth place with Arron Oberholser.