Shane Lowry and Brooks Koepka started off with a run of five birdies through seven holes of the Zurich Classic but trail the leaders by eight shots, while Séamus Power and partner Matti Schmid are just five shots off the top.
Offaly's Lowry, who won the tournament alongside Rory McIlroy in 2024, was doing the heavy lifting in the four-ball best-ball format in New Orleans as he was responsible for all five shots picked up between the second and seventh holes.
Koepka, who returned to the PGA Tour from LIV Golf at the start of the year, managed one birdie on the tenth and the pair failed to make inroads thereafter parring their way home to a 66.
That leaves the duo - the only pairing in the field to have both won a major championship - tied for 50th.
Waterford's Power, who had three birdies, and his German team-mate started on the back nine and shot a nine under to sit five shots off the lead held by American pair Alex Smalley and Hayden Springer, who combined for a 14-under 58.
Meanwhile, brothers Alex and Matt Fitzpatrick made a promising start as they carded an eight-under 64 in the opening fourballs.
The English pair, looking to become the first siblings to win the event, surged up the leaderboard when former US Open winner Matt made a hat-trick of gains from the 15th, only for both of them to bogey the par-five last.
Additional reporting: PA
