Frost, the South African who won the Toshiba Classic in March for his fourth Champions Tour title, had four birdies on the final eight holes to move to 12-under 205 in the major championship.
He said being able to sleep with the lead isn't the biggest thing about his situation.
''It's more just being comfortable with your game,'' Frost said. ''Getting into position like this makes you become a little more at ease the more you get there, but my game's been good this year.
''So I'm quite excited about (Sunday).''
Couples, the Presidents Cup captain and World Golf Hall of Famer, shot a bogey-free 68.
''I played the par 5s even, which is unusual for me,'' he said. ''I played them very poorly actually, made a couple of good up-and-downs to save pars. Then the other 14 holes, I played really well. I'd like to say I wasn't in too much trouble, basically because when I drove it in the rough, I judged my second shots pretty well out of the rough.
'(Sunday), I'm going to have to hit more fairways and play a little bit better from Tee to Green. When I did hit a good shot, it was a really good one and I made birdies.
He managed to save par on No. 6 when his drive went right into the creek.
''I can't sit here and kick myself,'' Couples said. ''I'm one behind Frosty. I'm in good shape.''
The final round will have a two-tee morning start because of expected rain.
Two-time defending champion Tom Lehman was five strokes back after a 69.
Frost hit a sand wedge from 80 yards to about 2 feet for birdie on No. 1. He missed a 6-foot birdie putt on No. 18.
Frost said he had an issue with mud on the ball only on No. 6 after rain forced a long delay Friday.
''But luckily I didn't have to go for the green there,'' he said. ''That mud made up my mind for me, and I laid it up and made a birdie from there.''
Hatalsky, who had his second straight 68, is a month removed from an opening 89 en route to a 23-over finish at the Insperity Championship. He said he switched irons and his driver this week.
''You just never know about this game,'' said Hatalsky, who finished with a 12-foot birdie putt. ''You go through the ups and downs. As a professional, you have to keep working at it and keep believing that what you're doing is the right direction. It's just a new week, and I'm enjoying it.''
After second-round leader Jeff Sluman and Waldorf each bogeyed on No. 4, there were 18 players within two strokes of the lead. Sluman's 72 left him four shots off the lead.
Corey Pavin delivered one highlight with a hole-in-one on the 173-yard eighth hole. He shot a 68 to finish at 6 under. It was his first ace since 2008 in the second round of the AT&T National.
''I've got the video in my head,'' Pavin said. ''I got up there and just hit a 6-iron right at it actually. I hit a really good shot and actually when it was in the air I said, 'Go in!' and it landed on the front fringe or right on the fringe on the green and just trickled and rolled in like a putt.''
Peter Jacobsen withdrew before the round because of a foot injury.