Tiger Woods and Padraig Harrington started the US PGA Championship at Hazeltine National as they finished the World Golf Championships-Bridgestone Invitational - locked in a duel at the top of the leaderboard.
Woods opened his account in the final Major of the year with a bogey free, five under par 67, while defending US PGA champion Harrington shot a 68 to throw down the gauntlet to the afternoon wave of starters including World Number Two Phil Mickelson, and 2009 Major winners Angel Cabrera, Stewart Cink and Lucas Glover.
"I was just very comfortable with what I was doing today," Woods said.
"The golf course is set up very fair. It's difficult but as Paddy (Harrington) and I were saying, you don't (usually) see pins, six, seven, eight feet from the side. It's normally three and four.
"So you can make birdies and be a little more aggressive going at these flags. You don't have to be as conservative."
Having gone toe-to-toe at Firestone Country Club last Sunday in the final round, Woods and Harrington were paired once more for the first two rounds alongside Rich Beem, the 2002 champion when last the event visited Hazeltine.
A triple bogey from Harrington last Sunday had decided their battle and handed Woods his fifth victory of the year and the World Number One, a four time US PGA champion, began the quest for his 15th Major looking for a third tournament win in as many weeks.
The pair matched hole for hole initially, both sinking birdies at their third hole of the day, the 12th, the Irishman thanks to a great approach shot to six feet and Woods with a 25 foot putt.
Woods stole a march on the 642 yard, par five 15th, getting up and down from a bunker but at the next hole Harrington caught up thanks to another good iron shot to six feet.
Harrington had his first stutter of the day when he bogeyed the first, his tenth hole, but bounced straight back with a birdie at the next hole to return to two under.
Woods also birdied the second hole to move to three under but was still lying one shot off the lead as Australia's Robert Allenby, American Michael Bradley and Alvaro Quiros all improved to four under.
Allenby birdied the 14th, Bradley the eighth and the big-hitting Spaniard made a three at the par four second but then all three dropped shots and who was waiting to pounce but Woods and Harrington.
Woods was the first to get to four under, with a birdie at the par five third, his 12th, and Harrington joined him there thanks to another good iron shot at the sixth, from where he made a birdie three.
Harrington missed a birdie opportunity at the seventh but Woods, having left his eagle putt short, made no mistake from three feet with a birdie putt to go into the outright lead at five under, parring his way home to the clubhouse lead in 67.
"The great thing when you play with Tiger is that you know you're going to have to play the shots," Harrington said.
"It puts you under more pressure and you feel like you might as well go after it rather than hang back.
"It actually helps you focus and you know you have to be on your very best form. It motivates you to play well."
US Ryder Cup player Hunter Mahan could have joined Harrington at four under but closed with a bogey five at the ninth for a three under 69 in the clubhouse alongside Australia's Allenby and Mathew Goggin and The European Tour’s longest driver Quiros.
World Number Three Paul Casey withdrew early this morning due to a rib injury, his place in the 156 man field taken by American Tim Petrovic.