Both players were on eight under par but only managed to complete three holes of the second round before rain, thunder and lightning brought play to an early halt.
It was later suspended due to a flooded course and will resume early on Saturday, organisers said.
New Zealander Fox carded seven birdies and an eagle for an opening round 64 to take a one-shot lead over Donald after the first round.
Fox is hoping to become the first New Zealander to be crowned Europe’s number one in the coming weeks having emerged as the closest challenger to Rory McIlroy at the top of the tour rankings.
Victory at Sun City would move him above his rival ahead of the season-ending DP World Tour Championship in Dubai.
Fox also birdied the par five second and then bogeyed the third at the start of his second round.
England’s Ross Fisher hit an eagle and three birdies as he blitzed around the first 10 holes before the rain fell, moving to six under par.
