Open champion Padraig Harrington returned to action for the first time since his maiden major victory at Carnoustie a fortnight ago and carded a two-over-par 72 at the WGC Bridgestone Invitational in Akron, Ohio.

That leaves him five off the shared lead, with Darren Clarke on level par while Paul McGinley is alongside Harrington on two-over.

Harrington began brightly with a birdie at his third hole, Firestone's 12th, but the Dubliner followed with three bogeys, including one at his last, the ninth.

"I worked hard," Harrington said. "I was disappointed not to par the last as I thought I'd got myself into the position where 71 would have been a very good return. But it's not the end of the world.

"I didn't play well today, didn't hit enough fairways but I didn't do myself that much harm that if I play well over the next three days I'll still be in there Sunday afternoon."

Paul Casey grabbed a share of the overnight lead with an opening three-under-par round of 67.

Teeing off from the 10th hole, the Englishman began his round with bogeys at the 12th and 14th before getting into the groove with a birdie at the 16th and carving out four more over the rest of his first round.

That leaves him tied in first place with American Hunter Mahan and South Africa's Rory Sabbatini at the head of the 83-man field, world number two Jim Furyk having withdrawn before play got under way with an upper back injury.

Defending champion Tiger Woods leads a pack of six players, including England's Lee Westwood, a stroke back on two under.

Justin Rose was one of five players a further shot back at one-under while Clarke, Ernie Els, Carl Pettersen and Anders Hansen were among a group of seven at level par on a congested leaderboard.

On one over par was Colin Montgomerie, who was left feeling confused following a "telephone number" back nine that still left him within striking distance of Casey's lead.