Clark, the 2023 US Open champion, sank a four-foot eagle putt at the par-five 16th on the way to firing a level-par 70 at windy Shinnecock to stand on seven-under 203 after 54 holes.Despite a three-putt bogey at 18, Clark boosted his lead by two strokes from his 36-hole margin."It was a tale of two people," Clark said. "I'd hit great shots and then I'd hit one of the worst shots and make dumb mistakes. Then I'd recover and make great putts or chips."The fact I increased my lead is a huge thing, so overall satisfied."The only golfer to lose a major with a lead of six or more entering the final round was Greg Norman at the 1996 Masters.Scheffler, who would complete a career Grand Slam with a victory Sunday on his 30th birthday, fired a 69 -- one of just two sub-par rounds on the day -- to claim a share of second on one-under 209."It would be special," Scheffler said. "This tournament means so much to me. All I can do is go out there and try and execute."Scheffler opened with two bogeys for only the fourth time in 105 major rounds, but birdied four of his first seven holes on the back nine before a bogey at the par-three 17th and a closing par."We've been battling hard for a few days and I did a good job of keeping myself in the tournament," Scheffler said. "I'll need a really nice round tomorrow if I'm going to try and catch Wyndham."Not since Lee Janzen in 1998 has a US Open winner been more than four strokes off the lead after 54 holes.Joining Scheffler on 209 were fellow Americans Sam Stevens and Sahith Theegala, whose tap-in at 18 was his lone birdie of the day, plus South Korean Tom Kim, who shot 72 after bogeys on three of his first six holes.