Australian Adam Scott edged one stroke clear of a congested third-round leaderboard at the WGC-Bridgestone Invitational on Saturday after a thrilling day of dazzling shot-making and low scoring.

While Tiger Woods was among those who failed to take advantage of surprisingly calm conditions at Firestone Country Club, Scott birdied four of his last seven holes for a sparkling four-under-par 66.

That left the 31-year-old Scott, who has Woods' former caddie Steve Williams on his bag, at 12-under 198 with compatriot Jason Day (66) and Japanese teenager Ryo Ishikawa (64) tied for second.

"Today was a good round because I wasn't really feeling it, although I'm swinging well," Scott told reporters after mixing six birdies with two bogeys around the turn.

"Just a couple of shots got away from me throughout the round, and I somehow managed to straighten it out early on the back nine and played really nicely coming in."

American PGA Tour rookie Keegan Bradley, one of six players tied for the lead late in the third round, carded a 68 to finish at 10 under alongside Britain's Martin Laird (67).

British world number one Luke Donald was among a group of three at nine under after an improved putting display helped him to a 64 but seven-times champion Woods was a distant 13 strokes off the pace after struggling to a 72.

The third round leaderboard in the elite World Golf Championships (WGC) event was always likely to be closely bunched with the greens highly receptive to approach shots after they were softened by rain earlier in the week.

Scott, Ishikawa, Day, Bradley, Laird and Swede Fredrik Jacobson were tied at the top late on before the Japanese edged a stroke clear when he sank a five-foot birdie putt at the 17th.

Moments later, though, Scott joined him at the top when he rolled in a 30-footer to birdie the par-three 15th.

The Australian then claimed the outright lead when he laid up in two at the par-five 16th before striking a pinpoint wedge to within two feet for a tap-in birdie.

SIZZLING START

He pared the last two holes to maintain the lead he had first established with a sizzling 62 in the opening round.

"It's a pretty bunched up leaderboard and a pretty tough golf course out there, but a couple of guys are going to play well," Scott said of Sunday's final round.

"I'm just going to have to play well to win tomorrow. A one-shot lead is not a lot over 18 holes."

Ishikawa, aged just 19, is bidding to become the second youngest winner ever on the PGA Tour. Should he triumph on Sunday, he would be just one week older than American Johnny McDermott, the U.S. Open champion in 1911.

"It's a little too early to think about winning this whole thing as of now but I do feel that I was able to play at a pretty high level today," Ishikawa said through an interpreter.

"Actually I am a little bit surprised how I performed out there. It has been a little bit hard for me to control the mental side of the game (on the PGA Tour) and I have had difficult times.

"But since the Masters (in April) when I was able to finish 20th, it has started to become fun to play here in the States."

Woods, who has generally reigned supreme at Firestone, was frustrated with his putting and driving accuracy after four bogeys and two birdies gave him a one-over total of 211.

"I didn't putt well again today but my iron game came back," the 35-year-old American said after totaling 33 putts in only his third tournament round in three months.

"I'm still struggling a little bit with my set-up and alignments off of tee shots because I used to curve the ball a lot more. Most of my shots are missing right on the edges of fairways so I've just got to get more committed to that."

Woods, who has missed the last two majors, is competing in his first event since he pulled out of the Players Championship in May after completing just nine holes.