The putt is one that Webb Simpson never practises enough. Yet he worked it to perfection.

From 70 feet and off the green on the par-5 18th, Simpson rolled in an unlikely eagle putt for an eight-under 63 to take a one-shot lead at the halfway point of the Dell Technologies Championship.

"You just kind of laugh at those because you're not trying to make them, you're just trying to get them close," Simpson said.

"The grass around the greens is firm enough to where the ball runs pretty smoothly. I didn't like my lie to chip it.

"I decided to putt it, and it came off really nice, just how I wanted it."

A gorgeous Saturday allowed for low scoring at TPC Boston and Simpson ended it at 11 under.

Tyrrell Hatton of England had eight birdies with his store-bought putter for a 63 and was one shot behind Wimpson, along with first-round leader Justin Rose (67).

Tommy Fleetwood made it a trio of Englishman near the top with his 65, leaving him three shots off the pace.

Australian Cameron Smith carded a five-under 66 - shooting a back nine 31 - to be tied fifth with Mexico's Abraham Ancer (69) at seven under while Marc Leishman is in a group of nine a shot further back after a second consecutive 68.

Adam Scott had two rounds of 71 to be even but his fellow Queenslander Jason Day missed the cut by five shots, finishing at seven over.

Double 2018 major winner Brooks Koepka (69) and world No.1 Dustin Johnson (69) trailed Simpson by six strokes.

Tiger Woods shot a 66 to stay in the picture, though he was seven behind Simpson at four under - in a group which includes Rory McIlroy (67).

"I've got some work to do still," Woods said.

"This is a golf course you can't sit still on. You have to keep making birdies. You have to keep getting after it.

"Conditions are going to be like this the rest of the weekend. You're going to see plenty of birdies out there."

Hatton is riding a hot streak with a $149 ($A205) putter that his caddie bought last week before the final round at Ridgewood Country Club.

"Obviously, he made a good choice," Hatton, too embarrassed to be seen in a golf store shopping for a new putter himself, said.