Clark had a collection of par saves around the turn as Scottie Scheffler was making a move and poured it on with a fairway metal to 4 feet for eagle on the par-5 16th for an even-par 70 that gave him a six-shot lead entering the final round.
No one has ever lost more than a five-shot lead in 125 previous editions of golf's toughest test. Greg Norman in the 1996 Masters is the only player to lose a six-shot lead in any major.
Shinnecock Hills did its part, even after the strongest wind subsided. Only two players managed to break par in the third round - Emiliano Grillo in 48km/h wind before the leaders teed off, and Scheffler with a 69.
Clark nearly joined them. After all his great saves, he missed a 5-foot par putt on the final hole and finished at seven-under 203, the lowest 54-hole score ever at Shinnecock Hills.
Now he has one more round to add another US Open title to the one he captured at Los Angeles Country Club in 2023. At his side will be Scheffler, the No.1 player in the world, trying to turn Sunday into a most magical day.
"I'm pretty satisfied with 70," Clark said.
"I feel good. I have got more and more comfortable every time I have got in these positions. I'm hoping I can bring my A-game finally."
At stake for Scheffler is a chance - a long shot at that - to complete the career grand slam, on Father's Day, which happens to be his 30th birthday.
"There's a lot of stuff going on," Scheffler said with a smile. "A special day. The tournament means a lot to me. Going to go out there and try to do my best and execute. I've been fighting like heck all week to stay in this tournament."
Scheffler, who fell nine shots behind with a pair of bogeys at the start, shot 32 on the back nine by chipping in from 65 feet on the 14th for the start of three straight birdies. His one big lament was missing a 4-foot birdie putt on the final hole.
He moved into the last group when Shinnecock Hills did a number on everyone else.Â
Sam Stevens, who closed within two shots of Clark on the front, started the back nine with three straight bogeys and closed with six straight pars for a 72. Tom Kim dropped two shots at the wrong time and shot 72. Sahith Theegala had one birdie, one bogey and 16 pars for a 70.
All of them were tied with Scheffler at one-under 209, leaving only five players under par.
World No.2 Rory McIlroy made five back nine bogeys en route to a 73, plunging to tied 17th at three over.
Fellow former US Open champion Matt Fitzpatrick slipped with a 74 to be tied 10th at one over.
12°C