Summerhays carded a four-under par 68 for a 13-under par total of 203. He failed to make the cut in his past three tries, which has never happened for him at any other PGA Tour stop.
Scott fired an impressive six-under-par 66 but at two-under remains a distant 12 shots back from American Dufner, whose second 65 rocketed him to 14 under.
He made four straight bogeys on the front nine and lost his five-shot lead in five holes. He started his back nine birdie-eagle-birdie-birdie.
His only blemish so far was a bogey on the par-four 18th in the first round, but the OH native claimed his revenge by sinking his second shot for eagle on that hole yesterday.
"I played great today", Summerhays said.
The former US PGA champion, seeking a fifth PGA Tour title, sits alongside Bubba Watson (68) and Justin Thomas (69). "Hopefully Muirfield Village has another good one for me tomorrow". He played through nerves, as well, in contending at the PGA at Baltusrol, won by Jimmy Walker. "There will definitely be nerves", Summerhays said of his expectations for Sunday's final round.
CHASING: Dufner was so smooth through two rounds and appeared unstoppable.
World No. 3 Ryu, who needs to finish at least third to have a chance to reach No. 1, opened with a three-over 74.
Is Osinbajo's visit to Calabar a bid to calm frayed nerves?
He commissioned the Calabar Monorail, the Calabar International Convention Centre, and the Cross River Garment Factory. Ben Ayade of Cross River's signature projects. "We are greater when we are together than when we are apart".
But he has not yet missed a putt from inside 10 feet, a feat he credits to recent work with a putting training device that has helped his consistency.
"I'd love to have two rounds in the 60s and feel like I've played solid golf going into Memphis and ultimately peak at Erin Hills".
"The tournament is not over", Dufner said. He shot 71 and was six shots behind.
After missing only five greens in his first 36 holes, Dufner missed his first four greens and finished the round having hit just 11 of 18. Coming off a 78 - and his first round without a birdie in almost four years - Johnson couldn't get anything going and shot 74 to miss the cut by five shots. I made some nice pars and rolled in some putts, " Dufner said.
Sun-splashed skies and calm winds yielded low scores in the first round of the Memorial Tournament at Muirfield Village Golf Club on Thursday.
Jordan Spieth was one shot out of the lead after the opening round but was already eight shots back when he teed off, and all he managed was a 72.
Taking the week off, Jutanugarn replaced Lydia Ko atop the ranking when So Yeon Ryu missed the cut.
World No. 3 Jason Day struggled, needing two late birdies to shoot a three-over 75. He wound up finishing one back of Kevin Kisner, and Spieth brought his form to Ohio.