Woods, who opened the third round with a five-shot edge, stands at 8-under-par 202 but Singh fired the lowest round of the tournament Saturday to get within two. Singh carded a 6-under 64 to reach 6-under-par 204 for the championship.
Tim Herron carded a 3-under-par 67 and is alone in third place at 5-under par. K.J. Choi bogeyed the 18th Saturday and fell into solo fourth at minus-4. Choi finished with a 2-under 68 in the third round.
Woods drove into a fairway bunker at the par-4 16th and his lay up landed in the first cut on the left side. He had 100 yards to the flag and misjudged the wind leaving his ball short in a greenside bunker. Woods blasted out 45 feet past the hole and missed his bogey putt but holed a 10-footer for double bogey.
'I just made mistakes I don't normally make,' Woods said.
Woods, the defending champion and winner of this event in 1999 as well, started strongly on Saturday with birdies at the first two par-3s on the course, Nos. 3 and 6. He sank a short birdie putt at the seventh to get six clear of Singh, who also tallied three birdies over his first seven holes.
Trouble loomed for Woods at the eighth as his four-foot par save lipped out on the right side. Singh ran home a 10-footer for birdie at the ninth to cut the gap to five shots.
Singh, who played two groups ahead of Woods, went on a tear around the turn. He drained a 10-foot birdie putt at 10, then holed a pair of eight-footers for birdie at 11 and 12 to get within two of Woods. Woods missed the green short at the 11th and his chip came up seven feet short. He missed the par save and suddenly his once enormous lead shrunk to one.
Things turned in Woods' favor as he birdied the par-5 12th and Singh missed his first green in regulation of the day at the 14th. Singh missed a five-footer to save par at his hole and Woods went three ahead. Woods extended the lead with a nine-foot birdie at the 13th but things got dicey for the No. 1 player in the world at 16.
Woods' lead was now one but Singh dropped a shot coming into the clubhouse. He drove into pine straw on the right side of the fairway at 18 and played his second short into a sand trap. Singh pitched his third 15 feet left of the hole but missed the par putt.
Woods had no chance at birdie at 17 but missed a 15-footer at the last that could have extended the margin. Most importantly, Woods holds the 54-hole lead and when that happens, Woods is 29-2 on the PGA Tour.
'It's not easy going out there with the lead because you know everyone is coming at you,' said Woods, who has four wins on the PGA Tour in 2003. 'But if I shoot the same score they do, I win.'
Singh would love to join Ed Fiori and Phil Mickelson as the only players on tour to beat Woods in the final round when Woods holds a piece of the lead with one to go.
'All in all, it was a good round,' said Singh. 'I'm really excited about tomorrow. I just have to go out and do the same thing I did today, tomorrow and I'll be okay.'
There is something more on the line Sunday afternoon than just this title. Singh currently leads the money list but if Woods triumphs, he would ascend to the top and become the only five-time winner on tour this season. Singh can join Woods and Davis Love III as the only four-time champions on tour in 2003 if he visits the winner's circle Sunday.
Basically, whoever comes out on top Sunday will probably have the inside track on Player of the Year honors.
'A lot of things are up for grabs tomorrow,' stated Woods. 'We'll just take care of business, play one shot at a time. Whatever the outcome is, the outcome is, but we've just got to play.'
'I am not going to focus on the money list,' said Singh. 'I am going to play hole by hole and do what I did today. I don't know if I can swing any better than this and if I keep doing this, I am going to shoot low numbers.'
Ignacio Garrido (69), Stuart Appleby (69) and Sergio Garcia (70) share fifth place at 2-under-par 208. Retief Goosen, who finished second in this event last year, shot a 3-under 67 on Saturday and is alone in eighth place at minus-1.
Paul Casey fired a 66 in the third round and is ninth at even-par 210, while Rocco Mediate (73) and Jerry Kelly (69) are tied for 10th place at 1-over-par 211.