England’s Chris Paisley kept his overnight lead and is on 15 under while Grace is second on 14 under.
Grace was five shots behind Paisley at the beginning of the round.
The Nedbank golf challenge winner didn’t start as well as he wanted to and after nine holes he was six shots behind Paisley.
Something clicked into gear on the back nine and he stormed up the leader board.
Grace made five birdies on the back nine and completed it in just 31 shots. He signed for a six under par 66.
Paisley completed his round in two under par 70 which included three birdies and one bogey.
Another South African Jacques Blaauw also carded a six under par 66 and he moved to 12 under for the tournament, three shots behind the leader.
Joining him on twelve under for the tournament is American Chase Koepka.
Koepka signed for a four under par 68 which included a birdie on the last hole.
It was a good day for scoring among the South Africans and Darren Fichardt carded the round of the day, an eight under par 64.
He’s in sixth place on his own on eleven under, four behind the leader.
Local amateur Kyle Mcclatchie also enjoyed the conditions and carded a four under par 68.
He’s on nine under for the tournament and joint 10th, six shots behind.