An established cross country exponent, the 34-year-old from Bryanston in Johannesburg led from just after the start to cross the finish line in the 40km event in a time of 1:36:44.
A short while later, Wessel Redelinghuys came in second in 1:38:05, with Josef Bester in 1:40:02.
Redhub rider Withaar said he had expected a tougher finish and was somewhat surprised that he was able to win relatively easily.
“In fact, before the start of the race, I went to have a look at the finish because I was expecting there would be a few guys together at the end.
“That didn’t happen, which surprised me.”
With defending champion Henry Uys in the group, Withaar was part of a five-man breakaway early on, but he used his expertise on the technical sections of the route to take the lead.
“I was surprised at how quickly the guys dropped off when things got a bit more technical.
“Obviously, with my cross country background, that’s the type of riding we do. With quite a few twisty trails, I was very comfortable on the route.
“I was on my own after about 15 minutes and from there I just focused on keeping my pace as high as I could for as long as possible. You can enjoy it so much more when you don’t have people on your back.”
Withaar enjoyed the experience provided by the route, saying it was far better than the trails created for several other mountain bike races in which he had recently competed.
“Previously we had ridden on mainly gravel roads, but that wasn’t the case here at all. I think the route was good, the tricky sections well marked and there was a good mix of everything.”
Withaar, who focuses on the national cross country events, said he used races such as the Land Rover West Rand Silverstar MTB Challenge to help him prepare during the off season.
“Basically we are in a building phase at the moment, training during the week and then using races such as Silverstar for that added intensity.”
The women’s feature event ended in a relatively comfortable win for Nadine Visagie of Cyclezone, who completed the 40km in 1:59:27.
Petruschika Constancon was runner-up in 2:07:51 with Tanya Hartley completing the podium in 2:10:50.
“The course was fantastic, not too technical, but just the right mix for a mountain bike race,” said Visagie, who made her third appearance at the race.
Johan Gouws won the 20km race in 1:08:57 with Chloe Gardner of Portable Shade taking the women’s title in 1:13:31.
For more results, go to Silverstar MTB Challenge.