Wyndham Clark surges clear as Rory McIlroy stays in BMW Championship hunt

Clark was one of five players who shared the overnight lead, but the American pulled clear of the chasing pack with a birdie at the 17th at Bellerive Country Club in St. Louis, Missouri.

The 32-year-old safely negotiated the final hole with a par from a fairway bunker to complete another flawless round and finish one shot clear of countryman Gary Woodland.

"Even though I missed some more fairways today, the misses were in good spots," said Clark.

"I feel like my putter still hasn't gotten hot yet, so it would be nice if it does on the weekend. But I played really good, solid golf."

Another overnight co-leader, JJ Spaun, briefly threatened to pull clear of the field after producing a blistering start. He reeled off four consecutive birdies on the front nine to build a substantial advantage and put himself in position to take control of the tournament.

However, Spaun's momentum stalled after the turn as he dropped three shots, allowing the chasing pack to close the gap. He recovered with a birdie on the final hole to card a six-under-par 66 and finish the day in outright third.

Chris Gotterup was a further shot adrift alongside South Korea's Im Sung-jae, with Michael Thorbjornsen and Patrick Cantlay another stroke back at eight under.

Rory McIlroy, meanwhile, remained within striking distance after carding a three-under-par 69 to sit tied for eighth, five shots off the pace.

The Northern Irishman is looking to rediscover his form after a disappointing 66th-place finish at last week's St. Jude Championship in Memphis.

McIlroy had a nervy moment on the second hole when he was forced to play his approach from the lakeside rocks, but managed to escape trouble and save par. It was one of 15 pars on a steady round.

"Today I hit some decent iron shots but was a little more squirrely off the tee," said the six-time major winner.

World No. 1 Scottie Scheffler, who cruised to a dominant victory at last week's St. Jude Championship in Memphis, battled through illness to produce a superb second-round 65.

After a disastrous opening round, Scheffler mounted an impressive recovery, making five birdies on the back nine to card a seven-under-par round and move to three under for the tournament.

"I'm a ways back, but I'm not out of it by any means," said Scheffler.

"I wasn't feeling a hundred per cent yesterday. I'll still not feeling a hundred per cent today. So I'll go home, get some rest.