Justin Thomas felt that it was the best he had driven the golf ball since he can remember during the third round on Sunday. Photo: John Bazemore, AP

US PGA champion Justin Thomas and Australia’s Marc Leishman surged into the third-round lead with impressive performances despite rain and chilly weather at the Dell Technologies Championship on Sunday.

Thomas was near perfect as he posted an eight-under 63 thanks to eight birdies, including one off a 49-foot putt on the par-four 12th hole, to stand at 12-under 201 with Leishman at TPC Boston.

“I was really patient going in to today,” said Thomas, who had the best round of the tournament, the second of the PGA Tour’s four FedExCup playoff events.

“I drove it really nicely. Best I’ve driven it since I can remember. It was a great day in tough conditions, I’m obviously very pleased.”

Leishman shot 65 with six birdies, three of them consecutively on the back nine. “When you’re not missing greens on days like this when the weather is tough, it takes a lot of stress off,” Leishman said.

“Really happy with the day, drove the ball well for the most part.”

The Australian hit 17 straight greens in regulation until the 18th. “I said to my caddie (on the 18th), ‘we could just hit to the middle of this green,’ but I wanted to try to make a birdie,” Leishman said.

“I actually hit a pretty good shot, but just spun it down and went into the rough.”

He recovered for a par.

England’s Paul Casey was a stroke back after a 67.

British Open champion Jordan Spieth (66), fellow American Grayson Murray (67) and Canada’s Adam Hadwin (68) followed at 10-under 203.

“On this golf course, you have to make birdies,” Spieth said. “Normally in the rain the scores are a little bit higher, but when Justin’s out there shooting 63, and the leaders at 12-under and you’re sitting there at (seven-under), you have to try to force it a little bit.

“Fortunately, it went the right way for me coming in. Birdieing 17 and 18 was large.”

World number one Dustin Johnson (66) and overnight leader Jon Rahm of Spain (71) trailed by another stroke at 204.

Thomas started his day with a birdie and delivered three more to make the turn at four-under. He continued his strong play with four additional birdies on his back nine.

The round was the third time this season he has scored 63 or lower. He had a 59 at the Sony Open in January and a nine-under-par 63 at the US Open.

The tournament concludes on Monday, with the top 70 players advancing to the penultimate event in the playoff series, the BMW Championship at Conway Farms in Lake Forest, Illinois in two weeks’ time.