Defending champ Padraig Harrington in action during practice day two at Turnberry Golf ClubEMPICS Sport

Padraig Harrington shot a first round 64 at the WGC-Bridgestone Invitational at Firestone in Akron, Ohio on Thursday to put him at the top of the leaderboard.

Harrington, who has spent much of the season retooling his swing and struggling badly, has missed the cut in four of his last six tournaments.

“I’m very happy. I feel that, especially at the end, I holed a couple of putts and that I got the most out of the round," said Harrington after the day's play.

“I have done a lot of work especially for the last eight months, I have been 100 percent focused on my swing, but maybe the last couple of weeks I have been back on track focusing on my game.

“I don’t know how the next three rounds will go but certainly for the rest of the year I know I will be a more competitive player."

Harrington had his best round of the year, shooting six birdies on a bogey free round. He leads Prayad Marksaeng, Tim Clark and Scott Verplank by two shots.

Tiger Woods shot a two under par 68 and lies four shots back.