Harrington is trying to win his third title on the PGA Tour

Ireland's Padraig Harrington made a superb start at the Wachovia Championship in North Carolina, firing an opening 66 for an early lead.

Harrington made six birdies and no bogeys to go six under par at the Quail Hollow Club, leaving him one clear of Vijay Singh and Jason Bohn.

Carl Pettersson and Trevor Immelman are in the group on four under.

World number one Tiger Woods returned to action for the first time since the Masters with a two-under-par 70.

Woods was playing on the first anniversary of his father's death.

I ended up using a new putter shaft this week and it worked wonders Padraig Harrington

The American world number one missed the Wachovia Championship last year in order to spend time with his father, who had been fighting cancer since 1998.

Woods, who had to contend with gusting winds in the afternoon, bogeyed the final hole to finish level with Phil Mickelson.

"I started out not that sharp, but I turned it around, played pretty good from number four on," he said.

"It got really difficult out there. These fairways, being this hard and fast and a little bit pitched and angled, it's really hard to hit some."

Harrington admitted he was not impressed with his all-round game but was happy with how well his new putter performed.

He used it just 24 times, making four of the six putts he faced in the 10-to-20-foot range.

"I didn't really hit the ball that well, or really have that much control, so it was definitely a round of good putting," said Harrington.

"I ended up using a new putter shaft this week, something that's quite revolutionary, and it worked wonders.

"It has two lead weights right at the top and it changes the dynamics of the putter substantially. It's so good it should be banned."

Defending champion Jim Furyk, South African Ernie Els and Sergio Garcia of Spain opened with 71s.

Lee Westwood and Brian Davis fired 72s and are the leading Brits on level par.

The strong field is boasting 27 of the world's top 30 players.