Boston - England's Paul Casey stuck to his game plan on Sunday with a five-under par 66 at the Deutsche Bank Championship, giving him a shot at just his second win on the PGA Tour.
The 39-year-old Casey stormed into Monday's final round of the second of four FedExCup playoff events by seizing a three-shot lead over American Brian Harman who finished with a 68 on Sunday.
"I am obviously over the moon," Casey said.
Casey closed his third round on Sunday with an eagle on the par-five 18th hole to finish 54 holes at 13-under 198.
Casey has 13 wins on the European Tour but just one victory on the USPGA Tour, defeating JB Holmes in a playoff seven years ago in Texas.
Casey surrendered his membership on the European Tour to play in America.
"There's still things we're missing and it hurts," said Casey. "But it's way better than it was, and so that's wonderful."
PGA champion Jimmy Walker shot a 70, placing him four back and in a three-way tie for third with second-round leader Kevin Chappell, who shot a 71, and Smylie Kaufman, who shot 68.
Ryan Moore is in solo sixth after posting a 68, putting him five adrift of Casey.
Northern Ireland's Rory McIlroy, who is ranked fifth in the world, vaulted into the picture with a 66 and is tied for seventh with South Africa's Louis Oosthuizen, who carded a 64.
Olympic champion Justin Rose of England shot a 69 and Tony Finau put up a 68, and the two are also tied for seventh.
McIlroy had a chance at an albatross on number 18. He came within three feet of a two with his 210-yard shot from the fairway. He settled for a tap-in eagle and finished with six birdies.
"It was worth the wait," McIlroy said of his eagle. "I had to back off the shot twice because the win was gusting and I didn't know if I had enough club in the end."
"Great way to finish the round, especially after making six at No 12."
World number one Jason Day busted loose after a slow start to the week by firing a 68. Day is 11 shots back and tied for 33rd place with Rickie Fowler and US Open champion Dustin Johnson.
The Australian capped his round with an eagle at No 18.
"The last couple weeks has been spurts of that guy (No 1 player in the world)," Day said.
Monday's final round tee times were moved up in anticipation of Tropical Storm Hermine's movement through the Boston area. Players will tee off in threesomes from the number one and 10 tees in 10-minute intervals.
Weather forecasters are calling for rain all day with possible wind gusts up to 80km/h.
Leading scores after third round of Deutsche Bank Championship at TPC Boston on Sunday (par-71, USA unless stated):
198 - Paul Casey (ENG) 66-66-66
201 - Brian Harman 68-65-68
202 - Smylie Kaufman 68-66-68, Jimmy Walker 68-64-70, Kevin Chappell 67-64-71
203 - Ryan Moore 65-70-68
204 - Louis Oosthuizen (RSA) 71-69-64, Rory McIlroy (NIR) 71-67-66, Tony Finau 67-69-68, Justin Rose (ENG) 68-67-69