They’ll lead the pack into the final round of the Regions Tradition.
Frost birdied the 16th and 17th holes Saturday en route to 6-under-par 66 and a one-stroke lead over Couples after the third round of the major championship at Shoal Creek.
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.
Couples, the Presidents Cup captain and World Golf Hall of Famer, shot a bogey-free 68.
Second-round leader Duffy Waldorf had 71 and is tied with Morris Hatalsky (67) and Michael Allen (69) at 206.
Augusta native Larry Mize had 69 and is at 211.
LPGA TOUR: In Pittsford, N.Y., Morgan Pressel slogged through rain and muck to take the lead after two rounds in the LPGA Championship. Next up is a 36-hole marathon today.
Pressel shot 2-under-par 70 at Locust Hill to reach 6-under 138 – two shots ahead of the top-ranked Inbee Park (68 on Saturday) and Chella Choi (73) in the second LPGA Tour major of the season.
EUROPEAN TOUR: In Atzenbrugg, Austria, Joost Luiten of the Netherlands shot 5-under-par 67, extending his lead to three strokes in the Lyoness Open.
The Spanish pair Jorge Campillo (66) and Eduardo de la Riva (69) are tied for second place.