INDIANAPOLIS, Indiana, Sept 8, 2012 (AFP) - Fijian veteran Singh, who held a one-shot lead after 36 holes, posted a three-under 69 to join Mickelson on 16-under 200 at Crooked Stick, where 70 players teed it up in the penultimate event of the US PGA Tour's four-tournament playoff series.
Mickelson and Singh, both World Golf Hall of Famers, will have plenty of quality competition on Sunday.
"I'm looking forward to tomorrow's shootout," Mickelson said. "It should be fun."
Northern Ireland's world number one Rory McIlroy, who won his second career major at the PGA championship last month, birdied 18 for a 69 to join Lee Westwood of England on 201. Westwood, a former world number one, carded a 68.
McIlroy leads the playoff standings that will determine the 30 players who advance to the Tour Championships that close the series.
"I'm in great position and excited about tomorrow," said McIlroy, who won the Deutsche Bank Championship last week.
"Phil obviously played well today... He might go out there and shoot the same number again tomorrow, but I just have to concentrate on myself and try and do the best that I can."
Australian Adam Scott carded a 66 for 202 where he was joined by Dustin Johnson (67) and Robert Garrigus (66).
Tiger Woods was three shots off the lead, alone on 203 after a one-under 71.
"It's an incredible leaderboard," Scott said. "It's going to be fun."
Woods appeared to aggravate his troublesome knee hitting from an awkward stance.
He was three over through his first eight holes with four bogeys and a birdie when a chip-in for birdie at the ninth ignited a string of three straight birdies.
He added another at the par-three 13th to keep himself in the hunt.
"I grinded hard," Woods said. "I didn't have much, and on top of that I made two really bad bogeys on seven and eight from the middle of the fairway, but at least I fought back where I have a chance going into tomorrow.
"It's probably going to take 63 or 64 tomorrow, but it can be done out here."
After a bogey at the third, Mickelson regained the stroke with a 14-foot birdie putt at four, then unleashed a string of four straight birdies starting at the par-three sixth.
His birdie at the par-five 11th moved him within one stroke of the lead and he tied Singh at the top with an 11-foot birdie putt at 13.
Mickelson's approach at 14 missed the green leading to a bogey, but he responded with a birdie at the next and closed with a seven-footer for birdie at 17 and a 15-foot birdie from the fringe at 18.
"It was a fun day. I got it going with the putter," Mickelson said.
Singh, who was four-under for the day through 13 holes, finished his round with three bogeys and two birdies in his last five holes.
"It was totally a mixed plate," said the 49-year-old Singh, who hasn't won on the US tour since 2008. "On the whole, I hit the ball pretty decent. I'm still in the lead, and I'm going to go out there tomorrow and see what happens."
Leading third-round scores here on Saturday from the $8 million BMW Championship (USA unless noted, par-72):
200 - Phil Mickelson 69-67-64, Vijay Singh (FIJ) 65-66-69
201 - Lee Westwood (ENG) 68-65-68, Rory McIlroy (NIR) 64-68-69
202 - Adam Scott (AUS) 68-68-66, Robert Garrigus 67-69-66, Dustin Johnson 68-67-67
203 - Tiger Woods 65-67-71
204 - Zach Johnson 67-69-68, Graeme McDowell (NIR) 68-67-69, Bo Van Pelt 64-69-71
205 - Louis Oosthuizen (RSA) 68-69-68, Chris Kirk 68-68-69, Ian Poulter (ENG) 68-68-69, Padraig Harrington (IRL) 70-65-70, Ryan Moore 66-66-73
206 - Jim Furyk 69-70-67
207 - Ben Curtis 70-69-68, Kyle Stanley 68-70-69, Justin Rose (ENG) 67-70-70, Troy Matteson 70-66-71, Bill Haas 71-64-72, Seung-Yul Noh (KOR) 68-66-73
208 - Ernie Els (RSA) 68-71-69, Brendon de Jonge (ZIM) 71-66-71, Graham DeLaet (CAN) 64-70-74
209 - Sergio Garcia (ESP) 69-69-71, Brandt Snedeker 69-69-71, Martin Laird (SCO) 69-68-72, Charl Schwartzel (RSA) 69-68-72, Steve Stricker 68-73-68, John Huh 70-66-73, Tom Gillis 69-67-73
210 - Luke Donald (ENG) 66-72-72, Matt Every 68-71-71, Rickie Fowler 67-70-73