Adam Scott extended his lead to three strokes in the St Jude Championship in Memphis after a 68 lifted him to nine under.

The Australian began the third round just one ahead of American Brian Gay but none of his nearest rivals could better his score, although David Toms' four-under 66 lifted him into a share of second place with Gay.

England's Brian Davis remains in contention after a second successive 68 left him four under.

Scott had a mixed front nine with two bogeys and a birdie but he improved after the turn, picking up three shots in four holes from the 13th. However, he refused to get complacent about his advantage over his rivals.

"Three shots is nothing really," Scott said. "That's a couple-hole turnaround out there. There's plenty of trouble to get in on this golf course. The pins are in quite difficult positions, and they have been every day. If you get out of position, it's hard to get back in.

"Three shots is definitely not a big enough lead as far as I'm concerned. It'd be nice to get off to a good start tomorrow and make it hard for them to catch me."

Toms had just one blemish on his card — a bogey at the par-four seventh — but he more than made up that with birdies at the second, fourth, 11th, 12th and 14th holes.

He is playing well but admits Scott, who won the Houston Open the week before the Masters, will be difficult to catch.

"He's the next superstar if he's not already," Toms said. "He's a nice fellow and good for the game of golf. He'll be tough. Obviously, he's won this year already. He played well last week. He's obviously on a roll right now."

Davis began with two birdies in his first three holes but then, after a further nine holes in regulation his round became more erratic. A bogey five at the 13th was followed by a double-bogey at the short next but he then carded three birdies in his final four holes to salvage his round.