The South African, looking for a maiden DP World Tour win in his rookie season, made four birdies on the front nine to get into a share of the lead after turning in 31 at the Taiheiyo Club Minori Course on Saturday.
Jarvis then enjoyed a huge stroke of luck on the 11th after his wayward tee shot bounced out of the trees, allowing him to save par.
He went right again off the 14th tee, but again bounced out on to the cart path, this time making the most of a drop to put an approach to tap-in range and the solo lead.
A closing birdie handed him a bogey-free 64 and a two-shot lead at 13 under, before German Yannik Paul also took advantage of the par-5 last to cut the gap to one with a 68.
"It would mean the world to win," Jarvis said.
"I've worked pretty hard for this, so I'll just go out tomorrow and stay patient and play every hole as it comes.
"It played pretty tricky, I don't find it very easy to get near these flags,, so I kind of played smart and just managed my game well around the course.
"I've been putting well this week, so I made a few good par putts. My goal at the start of the day was to go bogey-free, I did it yesterday and again today, which doesn't happen very often with me."
There was a group of five players two shots off the lead, one ahead of England's Matthew Southgate who signed for a 68.
Englishman Sam Bairstow had shared the lead after 36 holes but carded a third-round 71 to slip to nine under alongside countryman Will Enefer.
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