Akron, OH (My Sportsbook) - Padraig Harrington used a hot putter to fire a six-under 64 Thursday and take the first-round lead of the WGC-Bridgestone Invitational.

Harrington's 64 was his lowest round on tour this year and he leads by two strokes at the South Course at Firestone Country Club.

Tiger Woods, the winner last week at the Buick Open and a six-time winner of this championship, scrambled around for a solid round of two-under 68 Thursday.

He is tied for eighth place, but wasn't completely satisfied.

"Played all right, nothing great," said Woods. "I missed the ball in the correct spots and kind of hung around all day. You can go out there and be a little bit aggressive, you can get some numbers."

Woods was even through 11 holes with one birdie and one bogey, but a strong seven-iron tee shot left him 12 feet for birdie at the par-three 12th. He made that putt, then holed one from a similar length for birdie at the very next hole.

Woods played his final five holes in even-par although he had a decent look at birdie after a spectacular approach at the last. He settled for par and is right in the hunt.

Phil Mickelson returned to the PGA Tour for the first time since his tie for second at the U.S. Open with an even-par 70.

He missed significant time this summer while both his wife and mother battled breast cancer and his round on Thursday was his first action since the Monday finish at Bethpage, where he held a share of the lead in the final round.

"I was excited to get back out and play," said Mickelson. "I think surprising for me was I had been playing much better this week in my preparation. I had been driving the ball a lot better, I was swinging the club much more confidently."

Scott Verplank, who played with Harrington on Thursday, Prayad Marksaeng of Thailand, and Tim Clark are knotted in second place at four-under-par 68.

Steve Stricker, Zach Johnson and Ian Poulter share fifth place at minus-three.

They are chasing a three-time major champion embroiled in a disappointing season.

Harrington has undergone considerable swing changes this season, despite winning his second consecutive British Open last year as well as the PGA Championship.

"I didn't have any part of my game going so far this year," admitted Harrington, who hasn't had a top 10 in 2009 on the PGA Tour. "When you're making a change, you have to make sure some of it is good."

What was good for Harrington on Thursday was the putter. He needed only 27 putts in round one, but they covered quite a few feet of distance.

He birdied the 10th hole, his first in the first round, then waited six holes for his next birdie, which came at the par-five 16th.

Harrington opened his second nine with a birdie at No. 1 and made it two in a row when he converted a four-footer for birdie at the par-five second. That birdie tied Harrington for the lead and the Irishman extended it thanks to the flat stick.

After a bad approach into a bunker at six, Harrington only managed to blast out to 21 feet. He made that putt and moved to five-under par after a 26- footer for birdie at seven.

At the par-four eighth, Harrington's second stopped 23 feet from the flag stick. It hardly mattered to Harrington. He stroked home the birdie putt for his two-stroke cushion.

Guess the swing changes are working.

"The first six months had a purpose. I was working on things," Harrington said. "The last couple of weeks I was definitely more focused on my overall game. The first six months I was just focused on my swing."

Woods was joined in eighth place by Sergio Garcia, Hunter Mahan, Robert Allenby, Miguel Angel Jimenez and Danny Lee.

Defending champion Vijay Singh posted a 70 on Thursday and is part of a group with Mickelson tied for 27th place.

World No. 3 Paul Casey withdrew on Thursday due to a chest injury.