Grace caught fire on his back nine on Saturday after only posting a 71 in his second round which dropped him down the leaderboard but five birdies for an inward nine of 31 boosted his chances of bagging what would arguably be his biggest title to date on Sunday.
English duo Andy Sullivan and Matt Wallace carded three-under 69s to move to five under for the championship while former Ryder Cup victor Jamie Donaldson, who carded the first ace of 2018, is a further two shots back after a one-under 71 which saw the Welshman mix five birdies with four bogeys.
"I'm going to try and run with the momentum from the Nedbank Golf Challenge, be more patient, get things happening and not force anything", Grace said. "I'm just really excited about it".
Branden Grace achieved a career first of three eagles in one round as he opened with a 65 to share the lead on day one of the BMW South African Open, proudly hosted by the metro, at Glendower Golf Club, on Thursday.
And Jamie Donaldson recorded the first hole-in-one of this year's tournament when he aced the par-three 14th with a nine iron. "I thought I hit the ball superbly through 13 holes, but just couldn't get it in the hole".
The American, targeting a maiden European Tour success, is joined by Jacques Blaauw and Adrien Saddier on the same mark after rounds of six under and one-over par respectively.
"I really had no expectations whether I was going to play good or bad after having some time off", he said.
And he struggled through his first 10 holes on Saturday in just one-under-par before some inspirational words from his caddie and wife Nieke saw everything click as he collected five birdies in his last eight holes.
South Africa's Darren Fichardt is a shot further back after surging through the field with a brilliant 64 which featured eight birdies in the last 12 holes.
Compatriots Retief Goosen (209), after a disappointing 73, and Ernie Els, whose 70 left him on 211, appear out of contention for the top prize.