Tanaka stands at 12-under-par 132, one shot clear of Shaun Micheel, Lee Porter and Tommy Armour III. Micheel and Armour matched Tanakas 64, while Porter shot 67.
Armour first joined the PGA Tour in 1982. The 42-year-old has one tour title, the 1990 Phoenix Open. This is his second Q-School appearance since 1987.
'I'm happy with it, very,' Armour said of his position. 'Your job's on the line, you have to make the most of it.'
Tanakas round included eight birdies and no bogeys. He played in seven PGA Tour events this year, missing five cuts. His best finish came in a tie for 17th in the WGC-Accenture Match Play Championship.
Four more players made their way to double digits under par with four rounds to play. Robert Gamez (65), John Riegger (64), Kevin Durkin (68) and John Senden (67) are tied for fifth place at 10-under.
Seven players were tied at the top after round one; of those seven, none were able to break 70 Thursday at the Bear Lakes Golf Club.
Jaxon Brigman, one of the overnight leaders, followed his first-round 65 with a 1-under 71. Hes now tied for 17th place with six others ' including Blaine McCallister (68) ' at 7-under.
Ty Tryon, the 17-year-old high school student, shot 3-under 69 Friday to finish two rounds tied for 33rd place at 5-under. Gary Nicklaus is also at minus-5 after shooting 71.
Tryon started his day at 2-under, thanks to three birdies - all of which came on the par 5s - and one bogey in the first round. However, in round two, the teenager carded a bogey-6 at the par-5 12th (his third hole of the day).
Unfazed, Tryon played bogey-free golf over his remaining 15 holes, carding four birdies along the way.
'I played really good today, better than yesterday. I'm pretty happy right now,' Tryon said.
The top 35 scorers and ties following the sixth round Monday will earn their 2002 PGA Tour cards.
Full-field scores from the PGA Tour Qualifying Tournament