Australians Nathan Green and Stuart Appleby among six leaders after first round of US PGA Tour event

Australian Nathan Green conquered his nerves to complete a bogey-free 66 on Thursday, good enough to make him one of six players sharing the first-round lead in the US PGA Tour St. Jude Classic.

Green, who won his only US PGA title at the 2009 Canadian Open, has struggled with his game in recent years.

So finding himself in the lead midway through the round was an unfamiliar experience.

"I was starting to get nervous seeing my name on the board," admitted Green, who tapped in for his fourth birdie of the day at the par-5 16th, then parred the last two in a 4-under effort on the par-70 at Southwind.

He was joined at 4-under by compatriot Stuart Appleby, US veteran Davis Love, Glen Day, Martin Flores and Harris English.

Green was the only one of the leading group to play without a bogey. He admitted it was a welcome change of pace.

"Last few years, my game has gone a little bit south," he said. "I was always a really good chipper and putter, and I lost that part of my game almost totally. I am sort of rebuilding that."

Another 11 players, including defending champion Dustin Johnson and two-time St. Jude winner David Toms, were a stroke back on 3-under 67, with another nine on 68.

As crowded as the leaderboard was, four-time major champion Phil Mickelson did not figure on it.

Mickelson, playing in the $5.7 million ($A5.98 million) tournament with one eye on next week's US Open at Merion Golf Club, carded a 1-over 71.

"My short game was not good today," Mickelson said.

Mickelson opened his round with a promising birdie at the par-4 10th. But he bogeyed 15, where he missed the green and pitched 30 feet past the hole.

His second shot into the par-5 16th found a greenside bunker and he hit over the green with his third shot. After landing in the sand again, he ended up with a double-bogey seven, and followed that with a bogey at 17.

He clawed back with three straight birdies starting at the first, but capped his round with one last bogey at the ninth.

"I really feel like I'm striking the ball well," Mickelson said.

"The score obviously isn't very good... I'm looking forward to (Friday's) round because I know that ball striking-wise, it's about as good as I've been striking it and I feel like there's a good round in me."