Batting at number five, he made 52 from 157 deliveries as the visitors reached stumps on 192 for five.
They still trailed the home side by 60 runs, but it could have been far worse had it not been for a crucial sixth-wicket stand between Van Biljon and captain Werner Coetsee (44).
The pair batted for over a session together, putting on an unbroken 95, having initially come together with their side in serious trouble on 97 for five.
Simon Harmer (2-49) and Basheer Walters (2-26) took two wickets apiece.
The pair had also played a critical role earlier in the day when they managed to add 61 for the final wicket, the former ending unbeaten on 28 and the latter last man out for 33.
Malusi Siboto was the pick of the bowlers with six for 54.
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