The leader wasn't on his A-game for Round 3 but still carded a 5-under 67 after he posted back-to-back scores of 65 to begin his week at Sherwood Country Club.
Thomas will be looking to convert his narrow 54-hole lead into a 14th PGA Tour victory. He's eight for 13 when leading or co-leading after three rounds in his career, according to the 15th Club's Justin Ray.
To do so, Thomas will need to fend off the scorching hot Rahm - the Spanish native fired a 9-under 63 to tie Russell Henley for the low round on Saturday.
The two highest-ranked players in the field - Rahm and Thomas rank No. 2 and No.3 in the world, respectively - will be joined by Lanto Griffin to make up Sunday's final group.
Here's how the leaderboard sits ahead of Sunday's final round:
|Place||Player||To Par||R3 Score|
Patrick Cantlay remains the only player bogey-free for the week with his 4-under performance.
Sebastian Munoz, who led after Round 1, climbed back inside the top five with a 66.
While they sit well off the pace at 3-under par, there will be plenty of eyes on Tiger Woods and Phil Mickelson during the Zozo Championship finale. The two greats will tee off in the same group on Sunday at 2:28 p.m. ET, marking the 38th time in their careers they've played alongside each other on the PGA Tour, according to Ray.
Round 4 of the Zozo Championship begins at 12:38 p.m., with the leaders teeing off at 2:50 p.m.