The duo holds a one stroke lead over Ted Purdy, Guy Boros, Paul Claxton and overnight co-leader Craig Lile.
Quinn began the day at The Champions Club at 8 under par and in a tie for 28th. He began to climb the leaderboard with a chip-in eagle at the par-5 second, then converted back-to-back birdies from the fifth to move to minus-12.
He put together a pair of birdies around the turn at Nos. 9 and 10. He continued his assault with a seven-foot birdie at the par-3 12th and Quinn got to 16 under when he rolled in a birdie at the 15th from 12 feet.
The two-time winner on the Nationwide Tour two-putted for birdie at the par-5 17th to put him at minus-5 for the day, just on the four par-5s. He followed that with a kick-in birdie at the last to cap a bogey-free round.
'It was a great day of golf,' said Quinn. 'I hit the ball extremely well all day. I just want to go out tomorrow and do exactly the same thing I did today.'
Van der Walt meanwhile, posted five birdies on the front nine to quickly move up the leaderboard. He began with a birdie at the first and two-putted for another birdie on the fourth.
The South African rolled in consecutive birdies from the sixth to climb to 14 under. He closed out the front side with a birdie at the ninth.
Around the turn, he two-putted for birdie at the 10th to make it two straight. He followed that with birdies on the 11th and 12th for four successive birdies and van der Walt finished his round with six straight pars for a share of the lead.
'I was a 8 under through 12 holes so I'm a little disappointed in the round,' said van der Walt, who in search of his first Nationwide Tour victory. 'Overall I'm really pleased with the round and where I stand going into the final round.'
Van der Walt has not had a bogey in 36 holes and has just two for the tournament.
'I don't think I can ever remember playing 36 holes without a bogey,' van der Walt said. 'But today I was very disappointed in not birdieing two of the par- fives.'
Roland Thatcher fired an 8-under 64 to move to 16-under-par 200. He shares seventh place with Todd Rose, Bo Van Pelt, Eduardo Herrera and Sung Man Lee.
Jay Delsing, the defending champion, posted six birdies and three bogeys on his round. He shares 48th place with five other players at 9-under-par 207.