Thomas could have gone even lower as he narrowly missed birdie putts on the fifth and seventh holes, but he closed in style at the par-five ninth, where he hit a five-iron from a fairway bunker to 15 feet and coolly sank the eagle putt.
"It means a lot," the 23-year-old from Kentucky, who is seeking a third PGA Tour win in his last four starts, told Golf Channel after forging three shots ahead of fellow American Hudson Swafford and four clear of South African Rory Sabbatini.
"Any time you're in history, in any sport or whatever you're doing, it's a good thing. We all know it's a magical number in golf."
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Thomas, who clinched his third career victory on the PGA Tour at the SBS Tournament of Champions on Sunday, said he first had thoughts of shooting a possible 59 while playing his ninth hole of the day.
"It honestly entered my brain on 18th fairway when I had eight-iron in and I was like, 'You'd think I'm going to make birdie here and turn at six (under)," he recalled of his outward half of six-under 29.
"As well as I was driving it, I can go shoot six or seven (under) on this side and really, really post some history. But the two best putts I probably hit today didn't even go in, on five and seven.
"We (playing competitors Jordan Spieth and Daniel Berger) were talking about that and it was crazy how they didn't go in. Just enough went in, though, and that's all that matters."
Double major champion Spieth, like Berger, opened with a 65 but he was more than happy to play second fiddle to his good friend Thomas in the opening round.
"I'm just really, really happy for JT right now," said Spieth, who roared with delight after Thomas sank his eagle putt on the final hole, the par-five ninth. "It's history, it's awesome, it's really cool... to be able to watch it today."
Jim Furyk broke golf's magic number when he shot a record 12-under 58 at the Travelers Championship last year.
Al Geiberger was the first player to post 59 on the PGA Tour in 1977, followed by Chip Beck (1991), David Duval (1999), Paul Goydos (2010), Stuart Appleby (2010) and Furyk (2013).
(Reporting by Mark Lamport-Stokes in St Augustine, Florida; Editing by John O'Brien)
