American Roberto Castro chipped in from 80 feet for par at the 18th hole to remain in a four-way tie for the lead after Saturday's third round of the $6.5 million US PGA National.
Castro, whose best PGA finish is a share of seventh at the 2012 Greenbrier Classic, found the water with his approach on the final hole at Congressional Country Club but plopped the ball over a ridge and curled it into the cup.
"Saving a bogey would have been huge. Making a par is just a bonus," Castro said. "I thought I could just tumble it over the top of the ridge there. I told myself to be aggressive and get it back in there and it came out perfect."
The dramatic shot ended a par-71 round and kept Castro level with countrymen James Driscoll and Bill Haas and Argentina's Andres Romero on seven-under par 206 after 54 holes on a wild day that saw leader after leader falter.
Four players are the most to share a 54-hole US PGA lead this year.
Haas, a four-time US tour winner, had the low round among the co-leaders with a three-under par 68 but the roller-coaster ride featured nine birdies, three bogeys and a triple-bogey at the par-4 11th.
"Could have been a 6- 7-, 8-under day but it also could have been a 4-, 5-, 6-over day if I hadn't putted well," Haas said. "I'll take four or five birdies tomorrow and eliminate some mistakes and maybe win this thing."
Driscoll, seeking his first US PGA title, also shot a 68 while Romero, whose only US PGA title came at New Orleans in 2008, shot 70. American Jason Kokrak was on 207 with South Korean Charlie Wi and American Tom Gillis on 208.
Jordan Spieth, trying at 19 to become the youngest US PGA winner since 1931, opened birdie-birdie to pull ahead but a double bogey at eighth and a bogey at nine dropped him back. A round of 74 left him three strokes adrift.
Haas had four birdies and two bogeys in the first six holes, closed the front nine with two birdies, then tripled the 11th, the course's toughest hole. He followed with three birdies in four holes before a bogey at the par-5 16th.
"I don't really know what to make of how I'm playing other than I've got to take the positives and do some good things," Haas said. "I'm glad I made the birdies to make up for those bad holes."
Castro went bogey-double bogey at the second and third to drop back, then had back-to-back birdies on the two penultimate holes of the front and back nine with only a bogey at 11.
"I didn't think I was out of it. I knew I was still right in the mix," said Castro. "I knew that everyone was going to have a tough stretch. Mine just came early and I just tried to survive it."
Romero birdied four of the first eight holes and moved three strokes clear at one stage only to stumble with a double bogey at 11 and a bogey at 12.
"I played really well," Romero said. "I feel very comfortable. I (only) played two rough holes. I'm in great position."
Driscoll opened birdie-bogey, birdied the course's three par-5 holes and offset a bogey at 15 with a birdie at the par-3 10th.
"It's a tough golf course. It can come up and bite you like it did those guys," Driscoll said.
"I've just been real patient all week. I'm not exactly firing on all cylinders, but I'm just playing smart golf and not wasting any shots."
Wi, a five-time US PGA runner-up seeking his first tour title, charged into the hunt with a 65 that included nine birdies, seven of them on the front nine, his second nine of the round.
South Korean rookie Lee Dong-Hwan, who shot 75 to fall out of contention, made an obscene gesture toward a heckler that was shown by television cameras after his approach at the 12th hole went beyond the green on his way to bogey.