World number one Jason Day was poised to open up a big lead over his rivals at the US PGA Players Championship before his second round charge was halted by darkness.

The Australian star, who tamed TPC Sawgrass with a nine-under-par 63 in the first round, was on course for another low score after sinking five birdies before play was stopped with four holes left to play.

Day headed to the clubhouse on 14-under with his final four second round holes to be completed early Saturday.

Barring a late collapse, Day should take a healthy advantage into the final rounds over the weekend, with nearest rival Shane Lowry of Ireland three shots back on 11 under after two rounds.

Lowry backed up his opening 67 with another 67 on Friday, one stroke clear of three players on 10 under -- Sweden's Jonas Blixt, Germany's Alex Cejka and Cameron Tringale of the United States.
The top performance Friday came from American Colt Knost, who fired a superb nine-under-par 63 which included 10 birdies.

Only a bogey on the final hole -- when he missed a four-foot par putt that would have given him a 62 -- denied Knost a new course record.

"I was nervous over that last putt," Knost said. "So many great players have played this golf course, and to be the first one and only one to shoot 10-under would have been really cool."

Knost shares the TPC Sawgrass course record of 63 with Day, Fred Couples, Greg Norman, Roberto Castro and Martin Kaymer.

- McIlroy on the charge -

World number three Rory McIlroy fired an eight-under-par 64, getting off to a blistering start with five birdies and an eagle in his first seven holes.
McIlroy, a four-time major champion from Northern Ireland, was in the clubhouse on 136 after firing a par 72 in his first round, rising from a share of 83rd to level sixth, eight under for the tournament.

McIlroy opened round two off the 10th tee and sank a 26-foot birdie putt to start his seven-under 29 for his first nine holes, the course's back nine.

He followed with a four-foot birdie putt at the par-five 11th, a 14-footer at the 12th and then dropped his approach two feet from the cup at the par-three 13th to set up another birdie.

After a six-foot birdie putt at the 15th, McIlroy sank a 53-foot eagle putt at the par-five 16th to reach seven-under for the day and tournament. 

"I played well," McIlroy said. "The course was there for the taking. You really have to take advantage of it. Luckily I was able to take advantage of it."
"I'm a little disappointed the way I finished but 64 is still a great score," McIlroy said. "If I can get it out under par the next two days, I'll be happy. Conditions will be trickier. I don't think you'll see scores as low."

Knost sizzled at the start as well, a 17-foot birdie putt at the par-three third followed by four birdies in a row ending at the par-3 eighth. He added five birdies in seven holes in a run capped by a 13-foot birdie putt at the par-three 17th and needed only a par at 18 to break the record with a 62.

It was not to be, despite reaching his 18th green in regulation. 

Needing a two-putt par from 40 feet, he missed a curving left-to-right effort from four feet and settled for a share of the record with a 63.

"The toughest thing to do is when you try to two-putt and that's kind of what I was thinking, which I regret," Knost said. 

"I wish I would have tried to make it. It seems like every time you try to two-putt, you leave yourself something a little more than you want."

American Will Wilcox aced the par-three 17th hole. The famed island green had not surrendered a hole-in-one since Spain's Miguel Angel Jimenez made one in 2002.

Source: AFP