The 21-year-old Kinhult, ranked 183 in the world, maintained his two-stroke overnight advantage ahead of playing partner Chris Wood on 10-under-par for the tournament.
“It's going to be nerve-wracking, the first few holes, at least,” he admitted. “We'll see. I felt the nerves today for sure. Tomorrow is going to be the same I guess.”
Former Masters champion Garcia carded the round of the day as he looks to boost his hopes of automatic qualification for September's Ryder Cup, sinking eight birdies in a majestic 64 to reach seven-under and set up a mouthwatering Sunday pairing with world number five Rahm.
The big-hitting 23-year-old Rahm finished in style with back-to-back birdies, including a curling, downhill 35-footer at the last, and is four shots behind Kinhult.
The winner looks likely to come from that leading quartet, although USPGA champion Justin Thomas, who can retake the world number one ranking from Dustin Johnson with victory this weekend, is level with fellow American Julian Suri on four-under.