Xander Schauffele vaulted to a two-stroke halfway lead at the BMW Championship in Pennsylvania on Friday as Rory McIlroy and Tiger Woods slipped back in the second round.
American Schauffele hit 17 greens in regulation and used a hot putter for a six-under-par 64 on the Aronimink course west of Philadelphia.
The British Open runner-up posted a 13-under 127 total, while Englishman Justin Rose shot 63 to roar into second place on 11-under.
McIlroy and Woods, who shared the first-round lead, could not maintain their opening pace.
McIlroy plodded to a 69 to fall four strokes behind, while Woods (70) bogeyed the final two holes to slip five back.
Schauffele knows that nothing less than victory this week will give him a realistic chance of earning the final spot on the American Ryder Cup team.
But two more similar rounds could give captain Jim Furyk a dilemma.
On Monday, Furyk will make his final pick to complete the team to take on Europe this month. Tony Finau is considered the heavy favourite to get the nod.
Schauffele has not won this year. "It's not like I've had a bad year," he said after a round that included a 40-foot birdie at the 11th hole.
"I have given myself some good chances and here's another one."
As Schauffele took command, Woods went in the other direction as the old putter that he put back in the bag and wielded so well on Thursday refused to co-operate.
"It was just one of those days," he said after taking a profligate 33 putts. I hit it just as good and felt like I putted just as good. Just nothing went in.
"That's the way it goes. That round was easily six or seven under par, and I turned into even par, which is not what I needed to do today. Everyone's going low and birdies could be had."
Schauffele's closest threat, the ever-consistent Rose, had a seven-birdie 63.
A group three behind included American Rickie Fowler, making his comeback after missing the first two FedExCup play-off events while nursing a partial tear of an oblique muscle on the right side of his abdomen.
The top 30 players in the season-long standings after the BMW advance to the season-ending Tour Championship in two weeks.
Bryson DeChambeau, who won the first two playoff events, is assured of starting the Tour Championship as top seed.
Schauffele, ranked 41st, needs a strong weekend to advance to the season-ender.