Former world No 1 Jason Day is five shots off the lead after an opening 68 which included eight birdies and a double-bogey seven on the 18th, with Tour Championship victor Xander Schauffele a shot further back.
The 23-year-old, who is aiming to become the first Malaysian to win the Asian Tour Order of Merit, started the third round on the back nine and was on a high when he scored a birdie on the 12th and an eagle on the 14th.
FedExCup champion Thomas shares fourth on seven-under with Cameron Smith (68) while former world number one Jason Day faded with a two-over 74, dropping to 24th place and seven strokes off the lead.
Thomas made his fifth birdie of the third round at the closing hole to card a commendable two-under 70, which earned him a tie at the top with Scott Brown on nine-under par on a day when only 10 players managed to break 72.
"It was playing tough today", Brown said. "We'll hit some putts that look pretty stupid out there and the viewers at home don't understand". "It doesn't matter where you are, and I know that it is very cliche and easier said than done, but you just have to take advantage of the rest and time you have off the course".
Anirban Lahiri of India moved into a share of third place with Australian Marc Leishman (71) after a 69 that included four birdies and a bogey.
Gavin Kyle Green (pic) had a day to forget after shooting a disastrous second round 10-over 82 to rule himself out of contention of the CJ Cup in Jeju Island, South Korea.