Seamus Power dropped three strokes in his last four holes and lies three shots outside the projected cut mark after an opening 73 in the Fort Worth Invitational at Colonial.
The West Waterford man is tied for 102nd, 11 strokes behind leader Kevin Na after making two birdies, three bogeys and a double bogeys in a three-over-par round.
Na made an eagle and six birdies in an eight-under par 62 to lead by a shot from Charley Hoffman as Justin Rose shot 66, Rickie Fowler 67, Jon Rahm 68, Jordan Spieth a one-under 69 and defending champion Kevin Kisner a 72.
Power was two over after six when he three-putted the par-five first and failed to get up and down from the rough behind the pin at the sixth.
He made several good par saves on his front nine. But after getting back to level par by holing a 60 footer for birdie at the 10th and a six-footer for another at the 174-yard 13th, he double-bogeyed the 15th after flying through the green into water from the rough and then three-putted the 17th from 18 feet.
Na chipped in from 90 feet at his final hole to take the outright lead.
"It got over the ridge and I was like, 'This is going to be good. It's going to be close.' Then it catches the right lip," Na said after claiming his sixth first-round lead on the PGA Tour and his third at Colonial.
"This is a great golf course for me. Every year I come here I have high, high expectations," he said, before emphasising a note that had been relayed by a PGA Tour media official. "Did you hear what he said? I've had the lead a few times. He never said I won, did he?"
Na's best finish at Hogan's Alley was a tie for seventh in 2007, and his only PGA Tour victory came seven years ago in Las Vegas.
After starting the day with six consecutive pars, he hit a purple patch, picking up birdies at the 16th, 17th and 18th.
He then hit his approach to three feet at the 558-yard first and made the putt for eagle before holing a putt from close to 50 feet at the second to play that five-hole stretch in six-under.