Among the lessons Collin Morikawa found his reliable cut shot at Muirfield Village, and it sent him to a three-shot lead going into the weekend at the PGA's Workday Charity Open in Dublin, Ohio.
Morikawa ran off four straight birdies after making the turn Friday (Saturday AEST), finished with another birdie after the first of two storm delays and shot six-under 66.
He was six shots ahead when he finished, then was four ahead over Sam Burns when his side of the field finished.
By the end, it was down to three shots after some remarkable play by Justin Thomas (66) and Kevin Streelman (64) in surprisingly strong gusts that followed the storm.
Morikawa was at 13-under 131, one shot off the 36-hole course record set by Jason Dufner in 2017 at the Memorial.
Thomas hadn't made a bogey all week and finished his round with an eight-foot birdie putt.
Streelman reached 11-under until a bogey on the par-3 eighth near the end of his round.
They will be in the final group when play resumes, which will be played in threesomes because a pair of 75-minute delays from thunderstorms meant the second round didn't finish.
Sam Burns birdied his last three holes for a 66 and joined past Muirfield Village winner Hideki Matsuyama (68) four shots behind.
Right behind was Viktor Hovland, who took advantage of the tee being moved up on the par-4 14th.
His tee shot nearly went in and he settled for a tap-in eagle on his way to a 67.
Morikawa, with 15 birdies and an eagle through two rounds, is making his debut at the course Jack Nicklaus built, and perhaps it's no coincidence that Nicklaus was famous for hitting a cut.
"I had heard from a lot of people before, this course was going to suit a left-to-right shot, anyway," Morikawa said.
"Obviously, Jack hit that, and I think it does. But I've been able to leave myself some really good numbers into approach shots. I've been keeping myself in the fairway for the most part, and that obviously helps."
Australians Jason Day and Matt Jones shot 71 and 72 to finish the second round above the projected two-under cut on four-under and three-under, respectively.