Jim Furyk has a one-shot lead over fellow American Steve Stricker heading into the final round of the BMW Championship in Illinois.
Furyk wrote his name into the PGA Tour history books when he shot 59 in the second round and followed it with a solid 69 to finish 13 under par.
Stricker is second after shooting 64, while Brandt Snedeker and Tiger Woods are also in contention.
Luke Donald hit four birdies in his round of 67 to move to six under par.
Furyk, who was a surprise omission from the US team for next month's Presidents Cup, recorded three birdies after the turn in his third round before bogeying the last for a two-under round in favourable conditions at Conway Farms.
The 43-year-old narrowly missed a long-range birdie attempt on the 18th green that would have put him three ahead of the chasing pack, then missed a par putt from five feet to card his second bogey of the day.
Stricker, who holed out with a sand wedge from the fairway to eagle the par-four 15th, is alone in second, ahead of Snedeker (71) at 11 under and Zach Johnson (69), at 10 under.
World number one Woods was a further shot back in fifth, having briefly got to within two of the lead with an impressive run of six birdies in seven holes around the turn on the way to a 66.
Woods's momentum stalled when he bogeyed the driveable 15th after putting his tee shot into water, but he birdied the last to end his round four strokes off the lead.
Matt Kuchar had the best round of the day as he closed with three straight birdies to card a bogey-free 10-under 61 to surge up the leaderboard.
Donald is in contention for a top-10 finish after his round of four under but Justin Rose (69) could only move up two places to 26th spot.
Defending champion Rory McIlroy, 24, looked something like his old self as he shot a three-under-par round of 68 to climb out of last place.
The Northern Irishman's round, which included three birdies, an eagle and a double bogey, was a marked improvement on his previous efforts of 78 and 77 on the first two days
Lee Westwood, who has been playing catch-up after an injury-hit first day, also produced his best round of the competition with a two-under round of 69 to leave him nine over for the tournament in 66th place.
The BMW Championship is the third leg of four in the FedEx Cup end-of-season play-off series.
There is no halfway cut but only the top 30 players in the standings will qualify for next week's Tour Championship in Atlanta, where the FedEx Cup winner will claim a $10m (£6.3m) bonus.