Stockwell had Bryce Munro as a last-minute replacement partner after Danny Fowler had withdrawn from the three-stage race because of illness.
The two completed the shortened 36km first stage in 1 hour 39 minutes 17 seconds.
For Stockwell, who won the overall title with Fowler last year, today’s victory was especially pleasing.
“Even though the route had been shortened, it was quite technical,” he told In the Bunch. “I had a bit of a fall and hit my head after, I think, slipping on mud.
“There was not much in terms of wide roads; just a lot of single track and a rather hard climb towards the end.”
Stockwell said he and Munro had got together only yesterday after Fowler had dropped out with a chest infection.
“I was lucky enough to call on Bryce, who was able to fill in at the last minute. We started making plans only yesterday.
“We’d like to get ahead again tomorrow and enjoy some more single track. The routes are fun, but hard as well. That is what I love about this race.
“We hope to establish a good enough lead from the start, so that we can also enjoy some of the water points.”
Stockwell expects more technical and demanding sections in the last two stages of the race in the Cradle of Humankind.
“It is not your normal road race; there will be a lot of single track, which will be rocky and rustic.
“Today there was a rocky three-kilometre climb. That is probably why they made the stages a bit shorter, because they can be quite hard.
“It is actually a bit like a cross-country race and that is what I enjoy.”