De Groot and Williamson won the overall title in 10 hours, eight minutes and three seconds (10:08:03). London Olympian Candice Neethling and Swedish marathon champion Jennie Stenerhag finished second in 10:10:09, while Anriette Schoeman and Yolandi du Toit claimed the final podium spot in 11:03:21.
“It was good to race with Catherine. She is very experienced and we certainly seem to connect well on the bike and off it, which is important in mountain bike stage racing,” De Groot said.
“It’s great to finish off the year with a win. I’ve learned so much; especially in the races I didn’t win and will take that experience into 2015 with new goals. But first a proper break.”
Neethling and Stenerhag won the opening stage of the three-day race on Friday, with De Groot and Williamson coming in second. Third place went to Theresa Ralph and Jeannie Dreyer.
De Groot and Williamson came out blazing in the second stage, and did well to win the 64km route, opening a 48-second lead over second-placed stage finishers, Neethling and Stenerhag.
The final stage saw a thrilling battle in the women’s race, where De Groot and Williamson came out tops ahead of Neethling and Stenerhag.