Aiken shot a nine-under-par 63 with ten birdies and just one bogey, while Walters recorded a 64 – including an eagle on the 18th – as both players moved 17 under to hold a two-shot lead ahead of South Korea’s Jin Jeong.
Glaswegian Forsyth was in fifth place overnight after leading following the first round at Royal Johannesburg & Kensington Golf Club.
Joint halfway leader Craig Lee, from Stirling, dropped away from the leading pack into a 12-way tie for 18th – alongside England’s Ross Fisher – after shooting 74 as he doubled bogeyed the 12th hole as well as hitting three birdies and three bogeys.
Walters was pleased to put himself in a strong position ahead of today’s fourth round, and told www.europeantour.com: “I hit the ball so well today.
“Going into the day I just wanted to move forward a little bit, because my last attempt from this position I went quite backwards. I was aware of that and I made a strong effort to be aggressive today.
“I’ve got one more round tomorrow and I’m so happy that I’ve put myself into a strong position. I’m super excited for tomorrow, because it’s what we play for.
“Tomorrow is certainly a good opportunity, and I will be nervous, but, hopefully, I can improve on my record in South Africa.”
Three places at the Open Championship are up for grabs, along with a first prize of £170,000.
Italian former Ryder Cup player Edoardo Molinari, who was leading alongside Lee after the second round, also slipped down the leaderboard ahead of the final day’s play.
Molinari sits six shots off the lead following a third-round 72 in South Africa, suffering with bogeys on the second and third holes, and again on the 15th and 16th to sit eighth in the standings.
n Tiger Woods’ niece Cheyenne Woods is the outright leader at the end of the third day of the Volvik RACV Ladies Masters in Australia.
The 23-year-old is chasing a maiden Tour title and heads the field on the Gold Coast by one shot to Stacy Lee Bregman, with Minjee Lee two behind. Woods is 12 under for the tournament thanks to a two-under-par 71 yesterday.