Stephanie Houghton scored the only goal, curling home a superb 65th-minute free-kick which, given the nature of this 12-team competition, is almost enough to secure a quarter-final berth.
However, as the very first match GB have played in women's football, and the first event of the entire Olympics, Powell knows GB have made a statement that can never be erased.
"The girls have made history today," said coach Powell. "It has been mentioned so much we couldn't ignore it. We were the first women's GB team ever and we won. That will never change now.
"We wanted to enjoy the experience. We recognised it was the first event and that it was an opportunity for the girls to showcase their talent. I wanted them to embrace it and have a go. As it happens, we did alright."
Powell and her players have been overwhelmed by the entire Olympic experience so far. "It was a great crowd," she said. "It is nice to come to a big stadium. That inspires the girls to do well."
After a nervous opening, GB blew a succession of chances before Houghton stepped up for her big moment. It was some kind of redemption for the Durham-born defender, who has twice missed out on major tournaments because of injury.
"She has been really unlucky," said Powell. "She suffered major injuries before the World Cup in 2007 and the EUROs in 2009. She has worked really hard to get back into condition and is now one of the fittest players in the squad. Scoring today was a great honour for her."
Powell claimed Houghton was "in shock" as the ball went in, an assessment the 24-year-old did not dispute. "It is almost impossible to put into words," she said. "I knew I had struck it well and when I picked my head up it was in the back of the net.
"I didn't really know what to do with my celebration. I was trying to head towards the bench but I got tired and tried to slow down because it was so hot. It was a really special moment for me, the best of my career without a doubt."