Singh fired a six-under 66 to take over top spot on the leaderboard at 13-under par, one clear of Woods (67), McIlroy (68) and Ryan Moore (66) who sit at 12-under ready to pounce.
Bo Van Pelt (69) is joined by Lee Westwood (65) just two off the lead in a tie for fifth at 11-under, leaving four players who have been No.1 in the world inside the top six.
Adam Scott is the pick of the Australians in a tie for 13th, five shots off the pace after his second successive 68 left him at eight-under par.
"I played fine, not quite as nice as yesterday but I played good," Scott said.
Scott only needs a top 38 finish to advance to the season ending Tour Championship but needs a high finish this weekend to give him a legitimate chance at winning the FedEx Cup and the $US10 million bonus.
The Queenslander rolled in five birdies to just a lone bogey, gaining a stroke on all four par fives, as conditions remained soft and perfect for low scores.
His putting remained the biggest roadblock to lower scores - after two rounds he is ranked 59th in the 70-man field.
The 49-year-old Singh wound back the clock with a vintage display, providing just one bogey but knocking in seven birdies to light up the fans.
Having started on the back nine, the Fijian rolled in four consecutive birdies from the 18th through the third holes to leap ahead of the pack.
The Woods and McIlroy duel continued to excite the galleries, with 14-time-major champion Woods besting two-time major winner McIlroy by a stroke after being one behind on the opening day.
McIlroy had a rollercoaster round with an eagle, six birdies and four bogeys while Woods was slow out of the blocks but was bogey-free, collecting five birdies, three of which came in his final four holes.
"I've been able to grind," Woods said.
"I didn't have it with my swing, just kind of fighting it around here."
John Senden and Geoff Ogilvy are the next best Australians at five-under par in a tie for 33rd.
Senden is flirting with FedEx Cup elimination, currently projected at 30th, the last man in to the Tour Championship in Atlanta.
Ogilvy needs to make a big move, needing a top four placing to advance.
The season is all but over for Greg Chalmers (even par) and Marc Leishman (+4) as both needed top six placings to survive and are tied 59th and 67th respectively.
