BOSTON (REUTERS) - PGA Championship winner Justin Thomas and Australia's Marc Leishman surged into the third-round lead with impressive performances at the Dell Technologies Championship on Sunday.

Thomas was near perfect as he posted an eight-under 63 thanks to eight birdies to stand at 12-under 201 with Leishman at TPC Boston.

Leishman shot 65 thanks to three consecutive birdies on the back nine.

England's Paul Casey was a stroke back after a 67 for a 202 total in the second of the PGA Tour's four FedExCup play-off events.

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

World No. 1 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 the back side.

Leishman spread three birdies over nine holes to open play, then hit three in a row between the 13th and 15th holes.

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