Travelers Championship: Padraig Harrington three behind leader Jordan Spieth

Harrington won the Open Championship in 2007 and 2008, when he also won the PGA Championship

Ireland's three-time major winner Padraig Harrington scored a four-under-par 66 to trail first-round leader Jordan Spieth by three shots at the Travelers Championship.

American Spieth edged into the lead with a birdie on the final hole that sealed a seven-under-par 63.

Rory McIlroy shot a three-under-par 67, while England's Paul Casey finished on two under par with 68.

Defending champion Russell Knox of Scotland scored a one-under-par 69.

Harrington, 45, who won the Open Championship in 2007 and 2008, when he also won the PGA Championship, shot four birdies and no bogies on Thursday.

Spieth, the Masters and US Open champion in 2015, scored eight birdies and one bogey on what was his first appearance at River Highlands, Connecticut.

Early pacesetter Brett Stegmaier was reeled in and ended tied for second with fellow American Johnson Wagner, who like Stegmaier mixed seven birdies with a bogey.

World number four Jason Day of Australia scored a disappointing two-over 72 after three bogeys and one double bogey, with England's Luke Donald a shot further back on three over.