Anderson finished his round tied for 54th at even par; Harold Varner III is in 1st at 8 under; Brian Harman, Wesley Bryan, and Roger Sloan are tied for 2nd at 5 under; and Tom Hoge, Andrew Landry, Patton Kizzire, Billy Horschel, Bud Cauley, Nate Lashley, and Webb Simpson are tied for 5th at 4 under.
Varner picked up two early birdies and made four in a row around the turn as he peppered the pins with some precise approach play, and he added two more birdies at 13 and 15 but insisted he did not know he needed three further birdies to shoot 59.
Hoge made four birdies in a row on the front nine and six in all to go with a 14-foot eagle putt on the 15th hole to hold the lead at 9-under through 16 holes, but finished par-bogey.
Harris English led the chasing pack after he fired a 64, while former Masters champion Patrick Reed was one of a number of players to open with a 65 before play was suspended late in the day due to thunderstorms in the region.
"I get it. I get how it came across and I apologize for that", Koepka said.
A pair of major champions who challenged at the PGA Championship last week struggled in the opening round.
The world No.7 said fatigue was beginning to set in after playing in a slew of events recently and being in contention going into the final round of the PGA Championship in San Francisco on Sunday.
"A bit exhausted, to be honest with you, so definitely came out flat", said Koepka. I wish I would have thought about it, just to get some more goosebumps.
Koepka said even moving up a spot or two in FedEx Cup standings is helpful to advance, so that's why he passed up a week off to compete. He finished with three pars.
Varner, who went to high school in Gastonia about two hours away and college at East Carolina, was disappointed he couldn't play in front of friends and family because of the ongoing coronavirus pandemic.
"I played well here a year ago and I didn't think too much out there, it was just business as usual. Yeah, it's just good to be close to home". I was 9-under after 16 and thought I could birdie the last two holes, but I didn't hit the fairway.
Canadian Sloan was hot out of the gate with birdies on six of his first eight holes thanks to some stellar putting. 3 and 4 by making birdie at the par-5 10th and then the last hole at an event that is being played without spectators and in an isolated environment at the Renaissance Club in North Berwick.
Divots: The PGA Tour said there have been 510 tests for COVID-19 done at the Wyndham without any positives.