Pádraig Harrington shot a four-under-par 66 in the opening round of the Traveler at TPC River Highlands. The Dubliner managed six birdies and a couple of bogeys, no doubt relieved, like several others in the field, to have left the gates of Merion GC, home of last week’s US Open, behind them.

Hunter Mahan, who had a chance to win last week's Major going into the final round, carded a brilliant 62 to lead on eight under, but was later surpassed by Charley Hoffman, who had two birdies on the front nine before carding two eagles when shooting 28 on the way in.

Lee Westwood was also among the early finishers and he signed for a 67.

Mahan finished tied for fourth at the US Open last week after battling for the title down the stretch.

The 31-year-old, who started his round on the tenth, birdied his first hole before claiming three in a row on 13, 14 and 15.

A further birdie on 17 got him to the turn in 30 and three more on his back nine saw him record a flawless round as he looks to regain the title he won in 2007.

There was then a group of four players three shots back on five under as fellow Americans John Merrick and Webb Simpson along with Colombian Camilo Villegas and Australian Rod Pampling fired 65s.

Newly crowned US Open champion Justin Rose shot a three-under-par 67, despite a sloppy start that had him two over through six.

Bubba Watson, who finished runner-up last year and was champion in 2010, shot a 63 for seven under, while defending champion Marc Leishman was four under after a 66.