That’s the highest score any player has carded on the first day of the six previous U.S. Opens at Winged Foot, the world No. 3 finishing one shot clear of Patrick Reed, Thomas Pieters and Matthew Wolff and two clear of Rory McIlroy and Lee Westwood.
Thomas, 27, is looking to add to his sole major triumph at the 2017 PGA Championship.
“65 is fun no matter where you play, especially at Winged Foot,” he told reporters.
“I was in a really good frame of mind, and I was focused. I just was sticking to my routine and playing every shot, as opposed to getting ahead of myself.
“It’s one of those rounds where it’s just kind of like, next thing you know, you make the putt on 18, you’re done for the day.”
Tiger Woods, who has struggled for form since golf resumed earlier this year, finished on three-over after ending on a bogey and double bogey. He’s tied with world No. 1 Dustin Johnson, a pre-tournament favorite having clinched the FedEx Cup earlier this month.
Meanwhile, Phil Mickelson’s strained relationship with Winged Foot — where he let slip a U.S. Open lead on the final hole in 2006 — continues. He shot a nine-over 79.