Kitayama, who had started the day two shots clear of the field, had looked to have surrendered the initiative during a Jekyll-and-Hyde third round at Bay Hill in Orlando, Florida.
The journeyman -- who is chasing his first PGA Tour title -- looked to be in trouble after a double-bogey and a bogey saw him reach the turn at three over.
But four birdies down the stretch salvaged Kitayama's round, his 16-foot putt on the 18th securing an even-par 72 that left him one clear of an increasingly congested leaderboard on nine under.
"Really proud of how I was able to fight back to even," Kitayama said afterwards. "I've always just felt like there's no giving up. It's just kind of in my nature.
"Even when it's going bad, you can't just pack it in. You fight for every shot."
Until his birdie on the 18th, it looked as if Kitayama would have to settle for a share of the lead alongside Scottie Scheffler and Norway's Viktor Hovland, who are tied for second spot on eight under.
Scheffler's round caught fire with a hat-trick of closing birdies to complete a four-under-par 68 while Hovland conjured a brilliant six-under-par 66 to jump 18 places up the leaderboard.
After an erratic start that included three bogeys and four birdies, defending champion Scheffler ignited his round late on with a 16-foot birdie putt at the 16th before drilling a tee shot to within four feet at the par-three 17th.
After tapping in for birdie, he then picked up another shot on the par-four 18th when he nailed his second to six-feet.
Former world number one Scheffler said afterwards the secret to his success had been trying to stay patient after an erratic start to his round.
"I didn't want to put myself out of the tournament," Scheffler said.
"Around this golf course, as you see today, there's guys that have gone from very far behind to in the lead.
"Around this place if you can get hot you're never too far out of it. I just tried to keep reminding myself of that."
RAHM FADES, RORY LURKING
Scheffler will reclaim the number one ranking with a victory on Sunday if rival Jon Rahm fails to finish any better than solo second place.
A runner-up finish would be good enough for Scheffler if Rahm finishes worse than a tie for ninth.
Rahm's hopes of hanging on to the top spot faded on Saturday after the Spaniard posted a second straight four-over-par 76.
Rahm's nightmare round included a run of five straight bogeys between the seventh and 11th holes.
Hovland meanwhile produced another sparkling piece of iron play, chipping in from a bunker on the par-three 14th for birdie, as he compiled his bogey-free round.
The 25-year-old from Oslo had already holed out for eagle in Thursday's first round, and followed that up with an ace on the par-three seventh on Friday.
"It was just really, really solid," said Hovland, who finished second at Bay Hill last season behind Scheffler.
"I wasn't really close to making a bogey the whole day."
England's Tyrrell Hatton meanwhile moved 29 places up the leaderboard with a six-under-par 66.
Hatton saved the pyrotechnics on his bogey-free round for the back nine, where he rattled off five birdies to finish the day alone in fourth on seven under.
Rory McIlroy is also firmly in the hunt after a four-under-par 68 left him three off the lead on six under alongside Harris English.
Major winner Jordan Spieth and Justin Thomas are a further shot back on five under alongside Pierceson Coody.
