The impressive Nationwide Tour grad shot a 3-under 68 in the third round, making the last of his three bogeys after a poor chip at No. 18 and finishing the day with a two-shot lead over Aaron Baddeley.
Quinney, the 2000 U.S. Amateur champion and a former player at Arizona State, was at 16-under-par 197 for his first 54-hole lead on the PGA TOUR. He had led by three shots overnight.
Baddeley matched the low round of the day with a seven-under 64, trimming a six-shot deficit to just a pair of strokes despite hitting only five fairways Saturday.
He is 14-under 199 and looking to reverse a disappointing history at this event, where the Australian has missed the cut in three of his previous four starts.
'I think that because I live here I have put a lot of pressure on myself,' said Baddeley, who lives nearby in the same neighborhood as Quinney. 'This year I'm just enjoying it.'
Brett Quigley (66) and Bart Bryant (68) share third place at 13-under 200, with Vaughn Taylor (67), John Rollins (68) and Robert Garrigus (68) a shot further back at 201.
The second round was completed in the morning after play was suspended due to darkness Friday. For the second straight day there was a frost delay that pushed the first groups back.
Among those players who missed the 2-under 140 cut line were two-time winner Phil Mickelson and defending champion J.B. Holmes (both 141).
Quinney began his round with a 20-foot birdie putt on No. 1, then made a 4- footer for his second birdie at the third. He lipped out a 3-foot par putt at the seventh, but rallied with back-to-back birdies to finish the front nine in 32.
After making bogey from a fairway bunker at the 10th, Quinney strung together four consecutive pars while his lead was trimmed from three shots to one. He found another bunker at the 15th, this time blasting to within a foot to set up a birdie and move to 16 under.
In front of the raucous gallery at No. 16, Quinney knocked his tee shot right of the green and received a good-natured 'Boo!' from the thousands of onlookers at TPC of Scottsdale.
He shook it off, chipped within 5 feet and made par.
'You miss the green or you hit a putt short of the hole and you get a little criticized,' Quinney acknowledged. 'It's not really a flag you shoot at. I was just a little juiced up but made par and got out of there.'
Quinney rolled in a 3-foot birdie at the 17th, then gave away a shot at the 18th when he clubbed down to a 9-iron from 150 yards and came up short of the green.
With a pair of top-10 finishes in three events this season, he is getting used to playing late on Sunday.
'I'm going to look back at those, be able to be more comfortable and just approach the whole day in a different mind set, knowing that I can do it,' Quinney said.
Winning will take more than just confidence. There are 14 players within six shots of his lead heading into the final round.
'The greens are perfect, weather is perfect. I can't just go out there and shoot par tomorrow, I've got to make birdies,' Quinney said.
Baddeley made seven birdies in a bogey-free round and closed with a 20-foot birdie putt at the 18th. When he finished, he wasn't sure how close to Quinney he was.
He hadn't been looking at the leaderboard.
'Tomorrow I'll have a look because you've sort of got to have a look, but I'm just going to play golf,' Baddeley said. 'All I can control is my Titleist, and that's it.'