Australian Cameron Smith's blemish-free eight-under-par 64 catapulted him to the top of the leaderboard after the opening round of the CIMB Classic in Kuala Lumpur.
The former PGA Championship victor has a history for fast starts at the CIMB Classic, having shot no worse than 66 in the first round in his four appearances in Malaysia.
Smith, who won his first PGA title at the Zurich Classic team event in May, picked up five shots on the way out and three more over the last five holes to stand a shot clear of Thai Poom Saksansin and Americans Xander Schauffele and Keegan Bradley.
Thomas has thrived under sweltering conditions in Kuala Lumpur in the last two editions to rank No. 4 in the world, but stuttered in his final nine holes after erring with two bogeys.
If Justin Thomas is going to win his third straight CIMB Classic, he's got some work to do.
Smith scored eight birdies to become the solo overnight leader.
Smith followed a hat-trick of birdies from the third with gains at the seventh and ninth to reach the turn in 31, before rolling a close-range putt at the 14th and adding picking up shots at the 16th and 17th.
"I have to keep the game-plan pretty much the same really: just be smart off the tee, try to hit the fairways and then really aggressive into the greens".
One shot behind Smith are Thailand's Poom Saksansin, American Keegan Bradley and freshly crowned Tour Championship victor Xander Schauffele, also from the US.
Thomas has barely had time to pause for breath after a frenetic finish to the campaign and will take a proper break only after playing next week's CJ Cup, South Korea's first PGA Tour-sanctioned event.