The Sunshine Tour, who co-sanction the tournament along with the European and Asian tours, posted a photo on social media on Wednesday of Oosthuizen's bruised and swollen fingers.
She hung a broom on a tree outside the clubhouse and buried a fork at the base of the trunk while a colleague placed a glass of water upside down on a saucer above the fork.
The two-time European Tour victor kept a bogey off his card and made three straight birdies on the front nine before picking up four shots in six holes after the turn to vault into the share of second place.
The remaining 65 professionals (including ties) proceed to the final two rounds, which will be played on Saturday and Sunday at Firethorn Course.
"I don't know what to say".
"Obviously, I am very happy".
"When I played the Sunshine Tour event at Simola my little boy was sick with a bad chest".
"I was really looking forward to playing in the Joburg Open for the first time so I'm very frustrated".
Defending champion Darren Fichardt of South Africa opened with a three-over 75.
It also sees the field growing from 206 to 240 professionals, which means the stakes have been upped for the golfers aiming to clinch the prestigious winner's title, one of three qualifying spots for The Open Championship, or be among the prize money finishers of the tournament for their share of the R16.5-million prize purse.
After flying back after a T-7 at last week's AfrAsia Bank Mauritius Open, Oosthuizen injured a couple fingers when he got them stuck between two airport trolleys (baggage carts to Americans).