Dahmen's 62 at the Puntacana Resort's Corales Golf Course in the Dominican Republic was enough for a two-stroke lead over Keith Mitchell, England's Matt Wallace and South Africa's Garrick Higgo.
"I think just knowing my game's been there," Dahmen said. "We talked about it a little bit (at his practice round) on Tuesday, my game's been pretty good.
"It's kind of just letting it come to me and showing up on Thursday with the same intensity that I have on the weekend. I think I just did a really good job of that today."
Dahmen made five birdies on each nine and had three birdies in a row on three separate occasions.
Australian Aaron Baddeley fired a six-under 66 to be tied 10th and four behind Darmen.
Baddeley enjoyed a bogey-free round and blitzed the front nine, making five birdies before adding another at the 16th. Â
Dahmen's only PGA Tour victory came at the 2021 edition of this tournament. He has dropped to No.176 in the world rankings and has battled to get his game back in shape.
"I would say (missing) the Masters motivated me to get back on the golf course," Dahmen said.
"I had a sour taste leaving San Antonio with the missed cut there. I needed the week off, I needed the refresher, I needed to get back home and just relax and get my mind right for these four weeks in a row. So far so good."
Mitchell was already on the board with his eight-under 64 when Dahmen began his afternoon round.
"I've historically struggled teeing off in the afternoon when people go low," Dahmen said. "I feel like I'm teeing off eight back off the lead and I've struggled in the past of feeling like I'm playing catch-up already when I haven't even teed off yet."
Dahmen isn't the only past champion who enjoyed a strong start Thursday. Wallace, the winner here in 2023, carded eight birdies and zero bogeys.
"Got off to a nice start, holed a 25-footer on the first and I (said), 'OK, good to be back,'" Wallace said. "But I know - I kind of know what I need to do around here, I know what I need to do during the week.
"It definitely exceeded my expectation today. I've got kind of a score in mind each day and I managed to get to that pretty fast on that front nine."
Tied for fifth at seven-under 65 are Matt NeSmith, Chris Gotterup, Andrew Putnam, Quade Cummins and Japan's Rikuya Hoshino.
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