Britain's Tyrrell Hatton fired a one-over par 73 in a brutal third round at windy Bay Hill to seize a two-stroke lead on Saturday at the PGA Tour's Arnold Palmer Invitational.
The 28-year-old Englishman, playing only his second tournament since right wrist surgery in November, closed with a dramatic 31-foot birdie putt - only the day's third birdie at 18 - to stand on six-under 210.
"It was extremely tough out there," Hatton said.
"You could be made to look pretty silly at times without hitting too bad a golf shot. It was just amazing how much firmer the greens got throughout the day."
Top-ranked Rory McIlroy was hot on his heels after a difficult day in Orlando where the scoring average soared to 76.
"It felt like a US Open out there, so yeah, it was a good test," McIlroy said.
"I'm trying to enjoy it as much as I can."
Four-time major winner McIlroy, seeking a sixth consecutive top-five finish, shot 73 to share second on 212 with Australian Marc Leishman.
Another stroke back were South African Christiaan Bezuidenhout, South Korean Im Sung-jae, New Zealand's Danny Lee and American Harris English. None cracked par.
"I don't think anyone enjoyed that today," Hatton said.
"It was just so hard."
Hatton opened with a bogey but answered with a birdie at the third on a 22-foot hole-out from the fringe.
Hatton stumbled with a three-putt double bogey six at the ninth after finding a greenside bunker, sank a 28-foot birdie putt at the par-4 13th then fell back again with bogeys at 14 and 15.
"Most of the holes were crosswinds, so it was just so hard to get close," Hatton said.
"When the greens are as firm as they are, you've got no chance getting anywhere near some of the pins."
A tap-in birdie after a 33-foot eagle putt miss at the par-5 16th and the dramatic closing putt lifted Hatton into the lead, which matched the highest score to lead entering the final round in 42 years at Bay Hill.
"I was very happy that dropped," said Hatton of 18.
"Even though I tapped that putt it was probably going about eight feet past. It was scary how quick that thing was."
Hatton chases his first PGA Tour title but owns four European Tour victories, the most recent at last November's Turkish Airlines Open.
"There's doubles and triples just around the corner, so that two-shot lead can go extremely quickly," Hatton said.
"So for me there's nothing to get excited about."
McIlroy, who defends his Players Championship title next week, found a bunker at the par-3 second and missed a five-foot par putt.
But the 30-year-old Northern Ireland star rescued par from 18 feet at the third after blasting out of a greenside bunker and salvaged another par from the sand with an eight-foot putt at 11.
McIlroy, seeking his second Bay Hill title in three seasons, was just short on a 30-foot eagle bid at the par-5 16th. He tapped in for birdie to share the lead only to stumble at 18, finding left rough and rocks right of the green en route to a bogey.
"I feel good with my game," McIlroy said.
"Tomorrow it's all about keeping the big numbers off your card and trying to play as conservative as possible and pick up some birdies on the par-5s if you can."
Leishman, who won his fifth PGA title in January at Torrey Pines, birdied the par-5 sixth and 12th holes while making bogeys at the par-4 10th and 15th.
"Today's is probably as hard as I've seen this place play, which I enjoy," Leishman said.
"It felt like I shot 65 not 72."
Lee made an astonishing birdie at 12 after finding a bush left of the green with his second shot. He took a penalty drop on the 13th tee then holed out from 208 feet, lofting a shot over a tree onto the green and into the cup.
Leading scores after Saturday's third round of the PGA Tour's Arnold Palmer Invitational at Bay Hill in Orlando, Florida (USA unless noted, par-72):
210 - Tyrrell Hatton (ENG) 68-69-73
212 - Marc Leishman (AUS) 71-69-72, Rory McIlroy (NIR) 66-73-73
213 - Christiaan Bezuidenhout (RSA) 68-72-73, Im Sung-jae (KOR) 70-69-74, Danny Lee (NZL) 71-67-75, Harris English 69-70-74
215 - Kang Sung (KOR) 69-68-78
216 - Bryson DeChambeau 73-71-72, Patrick Rodgers 73-70-73, Matt Jones (AUS) 75-68-73, Collin Morikawa 70-71-75, Scottie Scheffler 67-74-75, Tom Hoge 70-70-76, Sam Burns 68-72-76
217 - Max Homa 72-75-70, Lee Kyoung-hoon (KOR) 72-73-72, Joel Dahmen 72-72-73, Keith Mitchell 68-75, Dylan Frittelli (RSA) 71-72-74, Charley Hoffman 70-73-74, Stewart Cink 72-70-75
218 - Jason Kokrak 71-75-72, Rory Sabbatini (SVK) 70-74-74, Troy Merritt 71-72-75, Bud Cauley 71-72-75, Matt Wallace (ENG) 69-73-76, Graeme McDowell (NIR) 68-74-76, Rickie Fowler 71-70-77, Brendon Todd 68-72-78