Keegan Bradley holed out for eagle from the fairway at his final hole on Friday to share the 36-hole lead at the Valspar Championship with fellow American Sam Burns.

Overnight leader Bradley's five-under 66  saw him keep pace with Burns, who fired five of his eight birdies on the back nine in a blemish-free eight-under par 63.

The US duo were four strokes clear of their nearest rivals with a record 36-hole total of 12-under 130.

South Korean KJ Choi had set the previous best 36-hole score at Innisbrook in Palm Harbor, Florida, with a 131 back in 2002.

"It was a fun day and what a way to finish. It was a blast," Bradley said after his gap wedge from 119 yards out at the par-four ninth tracked the pin all the way, landing just beyond the hole and spinning back in.

"I hit the shot and you can't see it from where we are, so you kind of have to wait for a reaction and then when people put their arms up, normally that means it goes in. But, wow, what an exciting way to finish," added Bradley, the 2011 PGA Championship winner.

Burns, chasing a first US PGA Tour title, hit just 10 of 18 greens in regulation but displayed a sparkling short game to produce the best round of the week.

His three birdies on the front nine included a 35-footer at the sixth. He rolled in an 18-footer from the fringe at the 10th to launch a run of three birdies in a row that was capped by his hole out from a bunker at the 12th.

A nine-foot birdie at 14 was followed by a 13-footer from the fringe at 15 that moved him to 12-under.

"I didn't even realize it was bogey-free," said Burns, who added that par saves from about six feet at the third and fourth were key to his day.

Burns's four top-seven finishes this season included a third place at Riviera in February, where he led after each of the first three rounds but missed out on the playoff won by Max Homa over Tony Finau.

Burns, 24, said the key for him this weekend as he attempts again to break through for a maiden title, is "just sticking to what I've been doing.

"I know over the weekend there will be some challenges, and I'm excited for the opportunity."

Homa was in a group sharing third on 134 along with former US Open winner Lucas Glover and Charley Hoffman.

Glover, seeking his first victory since Quail Hollow in 2011, had six birdies in his six-under 65. Hoffman also played without a bogey, nabbing five birdies in his 66.

Homa had an eagle and four birdies, but three bogeys in his final nine holes saw him sign for a three-under 68.

It was a further stroke back to five players tied on 135: South African Charl Schwartzel, South Korean Im Sung-jae, England's Tom Lewis and Americans Zach Johnson and Hank Lebioda.