Wyndham Clark moved into the solo lead with another bogey-free six-under par 64 at the BMW Championship Friday, with Rory McIlroy among the chasing pack at the second event of the PGA Tour's FedEx Cup playoffs.
One of five overnight leaders, Clark edged clear of the field with a birdie on the 17th after narrowly missing a long uphill eagle putt at Bellerive Country Club in St. Louis, Missouri.
A comfortable par from a fairway bunker on the last completed the 32-year-old's first-ever bogey-free opening 36 holes at a PGA Tour event.
"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."
Clark did roll in a 21-foot putt on the 14th, having birdied the fourth, sixth, eighth and 10th holes with pinpoint approach play.
The American, who won his second US Open title in June, hit the midway point at 12-under par, one stroke clear of former US Open winner Gary Woodland, who finished with back-to-back birdies after some wayward tee shots.
"I lost it a little bit on the back nine, lost some shots to the right, and I was able to adjust, kind of take a step back," said Woodland.
"I checked my grip and hit four really great shots coming in on 17, 18, so proud of the adjustment I made there."
Another overnight co-leader, JJ Spaun, had earlier built a substantial advantage with four straight birdies on a blistering front nine.
"Wasn't really thinking much. Was kind of in a nice flow mentally and technically with my game," he said.
Three bogeys after the turn gave hope to the chasing pack, before Spaun finished with a birdie for a round of 66 and third place, two shots behind Clark.
"That was a nice way to end the day. Kind of hit a little rough patch on 14, 15 with a poor 3-putt and a poor second shot on 14. But that's golf, it happens."
"I've always thought really tough courses fit my game... When fairways and greens in (regulation) are a premium, that's kind of where I do well, like a US Open," added Spaun, who won that major last year.
'SQUIRRELY' MCILROY
Chris Gotterup was a further shot back alongside South Korean Im Sung-jae, followed by Michael Thorbjornsen and Patrick Cantlay on 8-under par.
And fellow overnight co-leader McIlroy remained in the hunt, tied for eighth and five strokes back with a round of 69.
The Northern Irishman is trying to rebuild his form after an alarming 66th-place finish last week at the St. Jude Championship in Memphis.
He survived a precarious approach shot on the second hole, struck while teetering on lakeside rocks, to save one of 15 pars.
"Today I hit some decent iron shots but was a little more squirrely off the tee," said the six-time major winner.
Meanwhile world No 1 Scottie Scheffler, who marched to a dominant victory in Memphis last week, battled through a bout of sickness to bounce back from a disastrous opening round with an excellent 65.
His second round featured five birdies on the back nine, to leave him three-under for the tournament.
"I'm a ways back, but I'm not out of it by any means," said Scheffler, who admitted he had been struggling with an unspecified illness.
"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."