Ireland's Padraig Harrington played conservatively to retain the lead after Friday's second round of the 8.5 million-dollar World Golf Championships Bridgestone Invitational.

After shooting a brilliant 64 on Thursday, Harrington was solid rather than spectacular on a pleasant morning at Firestone Country Club, picking up just two birdies and one bogey in a one-under-par 69.

"I was a bit cautious at times (but) I suppose that?s only to be expected when you?re leading," the Irishman said after posting a seven-under 133 total.

Harrington enjoyed a one-shot edge over South African Tim Clark, who shot a 68, with veteran American Scott Verplank two strokes behind after a 69.

World number one Tiger Woods, a six-time winner at Firestone, shot a reasonable 70 to remain within striking distance, five shots back in a share of 13th.

Harrington, who won last year?s British Open and PGA Championship, has been mired in a slump this season while working on some swing changes.

He knows that some have questioned why he decided to change something that was working so well, but has never been one to listen to critics.

"I want to do it my way," he said. "That?s part of my nature. I?m not interested in standing still. I?m only comfortable being into my game when I feel like I?m improving. If I thought I was standing still, there?s no incentive for me to get out there."

Harrington hasn?t recorded a top-10 finish since January, but he can see some light at the end of the tunnel at last.

"I?ve found what I was looking for and that?s freed up my mind to go back to working on the important things - the scoring, the short game, the mental game," Harrington said.

"I normally play the first rounds cautiously. I was more worried about my misses rather than having that sort of confident attitude and going after a few more pins.

"I worked it around the course well. My short game has been good enough, so I probably should be a little bit more aggressive over the weekend. I would take breaking 70 two more times."

Woods, who also has gone backwards to go forward during a couple of swing reconstructions in his career, said he admired Harrington?s commitment.

"You have to make changes to get better and a lot of times you?re going to get worse before you get better," Woods said.

"You have to believe in what you?re doing, even though people tell you what you?re doing is wrong. I?ve been through that twice and think I?ve turned out on the good side both times."

Clark, last December?s Australian Open champion, was delighted with his score.

"The course firmed up quite a bit in the afternoon, so it was tougher to score," he said.

"It?s nice to see my game back to the level it was starting the year. This week I?ve tried to make sure I get it in play, get it in the fairway and from there I?ve been able to score.

"It?s probably boring to watch but I think it?s something you have to do."

US veteran Jerry Kelly and Spain's Alvaro Quiros shot 65 on a day when the field averaged 70.7 strokes, just a fraction less than during the first round.