Mennen and Hynek started the 67km seventh stage from Elgin to Lourensford wine estate in Somerset West, with a more than 10-minute lead.
They defended it comfortably finishing in a group containing their main general classification rivals for their maiden Epic title.
About 45km into the stage a group of four riders -- none in contention for the overall laurels -- broke away.
World cross country champion Nino Schurter of Switzerland and his South African team-mate Philip Buys (Scott-Odlo) turned up the pace with their back-up team of Matthys Beukes and Gert Heyns (Scott Factory Racing) --joining them.
The chasing pack, led by former Epic winner Roel Paulissen of Belgium and Riccardo Chiarini of Italy (Torpado) could not reel them in.
As the two teams approached the finish line on the grass at Lourensford, Buys and Schurter backed off, allowing the young South Africans to take the stage and make a piece of Epic history.
Four-times winner Christoph Sauser of Switzerland had started the day with Czech partner Frantisek Rabon (Meerendal Songo Specialized) determined to make inroads into the overall lead of Hynek and Mennen, but had to settle for second overall after being unable to shake off the Topeak-Ergon team.
There was some consolation for the Bulls team after losing race favourite Karl Platt to an injury when its back-up team -- Germans Tim Boehme and Simon Stiebjahn -- finished third overall.
Swiss national and Stellenbosch resident Ariane Kleinhans and her Danish team-mate Annike Langvad (RECM2) won the women’s category by more than 30 minutes, overturning a 24-minute deficit after stage one when they were plagued by punctures and mechanical problems.
Esther Suss of Switzerland and Briton Sally Bigham (Meerendal) finished second, while South African Theresa Ralph and Swede Jennie Stenerhag (Cape Brewing Company) were third.