Rory McIlroy claimed a one-shot lead at the halfway stage of the Deutsche Bank Championship thanks to a second consecutive 65 at TPC Boston.
Starting from the 10th, the USPGA champion birdied three of his first six holes before an eagle at the 18th completed a back nine featuring six threes.
Another followed for a birdie at the first and although he dropped shots at the next two holes, successive birdies at the fourth and fifth saw the 23-year-old from Northern Ireland finish 12 under par.
"Now that I'm in the tournament, I just want to play as well as I can and maybe reassess things going into the last day," world number one McIlroy said.
"But I was very happy with the two scores that I've got already and know that I need to go out and play just as good tomorrow to give myself a chance going into Monday.
"I got off to a nice start and sort of just kept the momentum going. Everything seemed to work pretty well out there.
"I felt like I drove the ball a bit better today and hit more fairways, which gave me some more opportunities to make birdies, and I was putting well enough to take a few of those."
Former Open champion Louis Oosthuizen was McIlroy's closest challenger on 11 under after also carding a 65, while American duo Ryan Moore and Tiger Woods were another shot back after rounds of 68.
"I didn't make anything today," said Woods, who missed all four of his putts between seven and 10 feet and three-putted the par-three 11th.
Overnight leader Noh Seung-Yul could not build on his opening 62 as he carded a level-par 71 to remain at nine under alongside Jason Dufner (66), Chris Kirk (70), DA Points (65) and former Masters champion Charl Schwartzel (65).
Schwartzel tore a muscle in his abdomen the week of the US Open and after finishing 38th at Olympic Club, took the next three weeks off to let the injury heel.
He returned to competition at The Open at Lytham and this week's event is his seventh in succession.
"I had the injury at the US Open and it set me back quite a bit," Schwartzel told www.pgatour.com.
"I came back, lost a bit of confidence, and am just seeing if I can play myself back into it.
"There's been great signs of it sort of from Wyndham, just finishing poorly on Sunday. Same thing at Bethpage, I was up there, finished poorly on Sunday.
"It's there. Once again, I can feel the game is great, so just a matter of finishing it off."
Padraig Harrington and Graeme McDowell are both two over par.