Seventy-four fellow golf professionals, Mother Nature and a nagging blister. All tried to hold Scott Piercy back Saturday at TPC Twin Cities in Blaine.

In the end it was the beast of the 18th hole that so many others have found cumbersome finally opening the door to misfortune just a crack to derail his momentum.

Staring into the last minutes of a fading sun, Piercy woefully mishit his second shot over the water. The splashdown led to a bogey but the 5-under-par 66 gives him a 3M Open 54-hole record 18 under, and a four-stroke lead going into Sunday's final round.

"The last four, five holes, kind of some tired swings and a little bit of mental grind," Piercy said.

Emiliano Grillo birdied the last hole to shoot 67 and assure a spot alone in second place. Doug Ghim's bogey-free 65 matched his best round of the season and vaulted him into third at 13 under, tied with Tony Finau. Fargo's Tom Hoge made a late charge with three closing birdies to put a bow on a 66 and sits alone in fifth place at 12 under.

That late blunder aside, Piercy put together an otherwise steady third round.

"If he brings half of his game from today to tomorrow, that's going to be very tough," Grillo said.

Already ahead by three strokes when play started bright and early because of expected severe weather, Piercy continued his dominance. He ran off five consecutive birdies on the front nine until horns blew halting play just before 11 a.m. More than 6 1/2 lightning-filled hours later, players were ushered back to the course to finish.

Piercy had just hit his tee ball on the par-3 eighth hole when PGA Tour officials decided to rush players and caddies off the course and pack fans into waiting shuttle buses. In the hour leading up to that Piercy made more than 50 feet of putts and put the rest of the field in his wake.

He faced a 60-foot birdie putt when play resumed and settled for par while favoring a coin-sized blister on his right heel, the byproduct of trying out a new pair of golf shoes Friday.

At times Saturday afternoon Piercy walked from shot to shot with nothing but a sock on the balky foot.

"Tried to do some stuff [Friday] night to doctor it up to get ready and just every move the shoe made was painful," he said. "So I just took it off. Didn't hurt to walk without it, so I just put it on when I hit and seemed to do okay."

Piercy is in much better position than just okay.

J.T. Poston, the winner at the John Deere three weeks ago, birdied four of his first seven holes Saturday and matched the round of the day with 7-under 64. Even that spectacular score leaves him nine strokes behind Piercy.

"He's in a position where he kind of controls the golf tournament," Poston said. "It's not playing too hard right now."

That was certainly the case early Saturday, when players teed off in threesomes off split tees starting at 6:50 a.m. In benign conditions and with preferred lies, the live scoreboards around the grounds soon showed bleeding red under-par numbers as the course played more than 2 1/2 strokes under par.

Tour rookie Greyson Sigg also shot a 64 and is tied with Sungjae Im in sixth at 11 under. Sigg made three long birdies in a row, including a 20-footer on the difficult par-4 ninth, as the clouds got darker with the bad weather moving in.

He waited out the delay with lunch and a nap. Sigg then played the final seven holes in 4 under.

After a run of five missed cuts in a row early this summer Sigg sits on the 125-player bubble, 126th in FedEx Cup standings. A strong Sunday would vault him into playoff status.

"Just shoot as low as possible," Sigg said. "Give myself as many looks as possible and, hopefully, see a few go in."