Singh's 69 was the low round on a windy day at The Ocean Course at Kiawah Island, which saw only five players break par.
Woods did most of his damage with his putter en route to a 1-under 71. Pettersson carded a respectable 2-over 74, joining Woods and Singh at 4-under 140 after 36 holes.
The stiff wind made for the highest single-round scoring average in PGA Championship history at 78 strokes.
Ian Poulter three-putted on No. 18 to finish with a 1-under 71, falling out of a share for first. The Briton instead finished alone in fourth place at 3-under par.