Scrumhalf Nic Groom added a third score in the second half, but the visitors were in the game until the final 15 minutes as they bagged tries through flanker Liam Gill, fullback Karmichael Hunt and winger Eto Nabuli.
Three penalties from replacement flyhalf Brandon Thomson, on his Super Rugby debut, and a late try from prop Vincent Koch sealed the game for the hosts, however, and ensured the Reds would have only one victory after nine rounds of the season.
An early penalty put the visitors in front, before Van Wyk scored the opening try after patient build-up from the Stormers.
Reds flyhalf Jake McIntyre got himself into a position to intercept the last pass to Van Wyk, but left the ball behind, allowing the winger to coast home.
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Zas showed good awareness when he picked up the ball at the back of a ruck close to the visitors’ line and was able to stretch and place the ball over the line.
The Reds got themselves back in the game when they profited from a basic error from Stormers fullback Cheslin Kolbe, who dropped a simple pass 10 metres from his line and from the resulting scrum Gill forced his way over the line.
Home flyhalf Du Plessis gave the home side a 17-10 lead at halftime with another penalty, but it was the Reds who scored first after the break through Hunt before Nabuli crossed in the same corner to put them ahead.
But the lead lasted a matter of minutes as Groom scored under the posts and Thomson added three penalties to open his account in Super Rugby and extend the gap to 11 points before Koch crossed the line in the final play of the game.
(Editing by Ed Osmond)
