One of five players tied for the lead overnight, the Fijian fired a four-under-par 69 on a second successive day of strong, gusting winds at a damp Kapalua Resort.
That left Singh at eight-under 138, narrowly ahead of his closest challengers, South Africa's Trevor Immelman (68) and American Will Mackenzie (70).
MacKenzie, among the pacesetters at the start of the day, briefly got to eight under with his fourth birdie but slipped back with a three-putt bogey at the par-four 17th.
"It was a little bit more difficult today to control your ball flight," former world number one Singh told reporters. "The wind was more gusty than it was yesterday.
"But I played very well. I like the way I'm striking the ball and I'm in control of my game, so I'm looking forward to the weekend."
The Fijian did well to avoid a faltering finish after he pulled his drive left into reeds at the last. Forced to take a penalty drop, he struck a superb third shot on to the green before two-putting to salvage par.
"I swung within myself all day and on that last hole I just tried to let one go and got quick," Singh said of his final tee shot.
"I hit a good drive there yesterday and made par and had a bad drive today and made par, so it kind of evened out."
Immelman, the 2006 PGA Tour rookie of the year, surged into contention with two birdies in the last three holes.
"I was really happy with my consistency today," the 27-year-old said after rattling up six birdies and one bogey.
SWING RHYTHM
"I think the rhythm of my swing has been the key to my play
Big-hitting American J.B. Holmes, who matched Immelman's best-of-the-day 68, was tied for fourth at five under after vaulting up the leaderboard with four consecutive birdies from the par-three 11th.
"I missed a couple of short putts coming in on the front (nine) but played really well on the back side," Holmes said after finishing level with compatriots Davis Love III (71) and Chris Couch (70).
Holmes, who booked his place in the winners-only event with victory at last year's Phoenix Open, played on his own after compatriot Arron Oberholser withdrew due to a bad back.
Australia's Stuart Appleby, bidding for a fourth successive victory at Kapalua, was seven strokes off the pace after carding a 72.
Singh picked up his first shot of the day at the par-four third after hitting his approach to within five feet of the flag.
That earned him a share of the early lead with Canada's Stephen Ames, who broke clear of the overnight logjam with a birdie at the opening hole.
Although Singh briefly slipped back with a three-putt bogey at the fourth, he forged one ahead of the pack after reaching the green in two at the par-five fifth and holing a 20-footer for eagle.
The smooth-swinging Fijian, runner-up at Kapalua twice in the last three years, also birdied the 14th and 15th to stay in control of the tournament.
Preferred lies were in operation after the start of the second round was delayed by 80 minutes because of strong winds and driving rain.
This week's event launches the inaugural FedExCup, a season-long points competition culminating in a four-event playoff series with $10 million to be won by the overall champion.