In addition, Gwin brought the United States its first downhill World Cup win since 1999. His achievement marked the end of a long drought which had followed a period of American excellence in the early days of competitive mountain biking.
"I'm pretty speechless actually. It's a dream," said Gwin.
For Moseley, it was her first World Cup win in the coveted rainbow jersey of the world champion.
In qualifying, Gwin placed seventh. He spent much of the remaining time working with his team's mechanics to find the ideal set-up for what was going to be a much faster and drier race.
It was Gwin's eighth World Cup podium finish, but his first win, especially important as it came in his first major race with his new team. Gwin made the jump from Yeti with the start of the new season.
"In the first sector [of my final run] I made a little mistake, hitting some trees with my shoulder, but then I just regrouped and put as much power down as I could in the middle sector," said Gwin.
"By the end, the legs were really feeling it, and then it was a pretty nerve wracking waiting in the hot seat. The whole time here in South Africa with the team has been so great."
Moseley had done the same thing in 2009 - won the Pietermaritzburg opening World Cup in her first race for the team. This year's 2011 victory was her 13th career World Cup win and her third for Trek World Racing. Moseley was probably the only downhiller racing the World Cup who had competed in the Cape Epic mountain bike stage race just a few weeks ago. She said the fitness she attained during that event paid off.
After winning qualifying on Friday by nearly six seconds, the finals proved a tighter affair - she won by 0.28 seconds. The course was running about 15 seconds faster for the women and the effort to get the bike to the line was huge.
"That was so tough. Towards the end I was running out of steam and had the rear kick up on something in the lower section of the track," said Moseley.
"Then I heard the onsite commentary say it was going to be close, so I dug deep until the end. It means a lot to win my first World Cup at my first attempt since earning the world champ's jersey, it just means so much."
Trek World Racing's team director Martin Whiteley said, "Three years ago Trek, like Aaron, wasn't racing at the top level of World Cup downhilling. Here we are today with clearly a winning package, and I can't speak highly enough of the engineers in Madison, and our key sponsors who give our talented athletes such an amazing set up to do their job. I'm so proud of everything this team has done since we arrived in Africa four weeks ago, and I'm really looking forward to a thrilling 2011 season".
While the team's cross country racers will be busy at May World Cups in Dalby, United Kingdom and Offenburg, Germany, the next downhill World Cup isn't for six weeks. Round two is set for Fort William in Scotland. Until then, the downhillers will be based on the East Coast of the United States.
"[I] can't wait for Fort William, I love that track," said Gwin, who will sport the World Cup leader's jersey on June 4-5.
See Cyclingnews' full coverage from the UCI Mountain Bike World Cup in Pietermaritzburg, South Africa.