Kevin Chappell birdied three of the last five holes to snatch a one-shot lead as strong winds sent scores soaring on the third day of the Valero Texas Open.
Only two of the remaining 76 players managed to break 70, while nobody managed to negotiate the AT&T Oaks course at TPC San Antonio without at least one bogey on their card on a brutally tough day.
Chappell defied the conditions to card a one-under 71 which earned him the outright lead on eight under par, with Branden Grace and John Huh just a shot adrift heading into the final round which is expected to be played in similar cool and blustery weather.
An erratic outward 38 saw Chappell slip down the leaderboard as he offset three birdies with three bogeys and a double-bogey at the sixth, where a wayward drive left him no option but to pitch back to the fairway before dumping his third into a greenside bunker.
But the 30-year-old, chasing his maiden victory on the PGA Tour, steadied himself with a solid run of pars after the turn and he followed a birdie at 14 with a rare two at the par-three 16th after his tee shot kicked off the left bank and rolled to 12 feet.
Chappell got up and down from short of the green at the driveable par-four 17th, and he came close to finding water with his lay-up at the last before doing well to two-putt from 65 feet to ensure he would sleep on the lead.
Grace had earlier set a stiff clubhouse target at seven under after the South African carded a commendable two-under 70 featuring four birdies and just two dropped shots.
He was joined in a share of second by Huh, who was two over for the day until he holed his bunker escape for a thrilling eagle at the 17th and he added a birdie at the last to salvage a battling 71.
Ryan Palmer had earlier propelled himself 32 places up the leaderboard with the low round of the day, a superb 68 which included three birdies in four holes on the front nine before he responded to his only blemish at 13 with birdies at each of the final two holes.
Palmer closed on six under along with veteran Swede Carl Pettersson (71) and big-hitting Scot Martin Laird, who could have been closer to the lead had it not been for a scrappy double-bogey six at the 12th and a further dropped shot at 14.
Laird regained his composure to produce a birdie-birdie finish for a 71, while overnight leaders Tony Finau and Bud Cauley stumbled to 74s to slip to six under alongside Palmer, Pettersson, Laird, Kevin Tway and Cameron Smith.
But former US Open champion Graeme McDowell (76) and fan-favourite Andrew "Beef" Johnston (74) will be playing for pride on Sunday as they ended a difficult day on two over par.