- Becomes youngest player to shoot sub-60
- Joins seven others to score in 50s on PGA Tour
The 23-year-old won the Tournament of Champions on Sunday and backed it up Thursday with a first-round 59 courtesy of an eagle on his last hole at the Sony Open in Hawaii.
The lowest round on the PGA Tour is the 58 of Jim Furyk, recorded at the Travelers Championship last June.
The previous youngest of the seven players to go under 60 was the 27-year-old David Duval in 1999.
"Any time you're in history, in any sport or whatever you're doing, it's a good thing," Thomas told the Golf Channel from Waialae Country Club.
"We all know it's a magical number in golf."
Thomas joins six other players to have shot 59 -- Al Geiberger, Chip Beck, Duval, Furyk (in 2013), Paul Goydos and Stuart Appleby.
Two-time major winner Jordan Spieth, a close of friend of Thomas, said after Sunday's win: "I think it's potentially floodgates opening for him.
"The guy hits it forever. He's got a really, really nifty short game. He manages the course well."
Thomas, from Louisville, Kentucky, has won once in each of the last three seasons on Tour after turning pro in 2013.
His best finish in the six majors he has played is tied 18th at the 2015 US PGA Championship.