A birdie on the last hole saw Jordan Spieth take sole possession of the early clubhouse lead at the Travelers Championship in Connecticut, with Irish pair Rory McIlroy and Padraig Harrington also firmly in contention.
Former world number one Spieth signed for a seven-under 63 on his debut at TPC River Highlands, with a bogey on the 406-yard ninth preventing him from securing more than a one-stroke advantage.
Local hopeful Brett Stegmaier was the early pacesetter and reached Thursday evening tied for second with fellow American Johnson Wagner, who like Stegmaier mixed seven birdies with a bogey.
Canadian Graham DeLaet had an eagle on the fifth to thank for his lofty position just outside the top three while Idaho-based Troy Merritt also carded 65 after recording four birdies on the front nine.
Dubliner Harrington, making his return to action following a freak elbow injury suffered during a coaching session, admitted: "I surprised myself" after shooting flawless round of 66.
McIlroy matched Harrington by firing four birdies, but a bogey at the 18th, his ninth hole, left him one shot behind his fellow Irishman at three under.
The Down native, who last week - for the second year running - missed the halfway cut at the US Open, underhit a putt from three feet.
Seamus Power shot a two-over par 72.
