Steph Houghton's third goal in as many games was enough to maintain Team GB's flawless Group E campaign at London 2012 on a record-breaking night at Wembley.
Such was the magnitude of the result, Powell's players and the 70,584 crowd - by far the largest ever for a women's game in Britain - celebrated at the final whistle almost as if a gold medal had been won.
But their manager was as stony-faced as ever and urged caution ahead of Friday's quarter-final against Canada in Coventry.
"Every game, we've done well, we've won the game, we've topped the group," she said. "The danger is that everybody starts jumping on this 'medal'. We still have to play Canada. They want a medal as much as anybody else.
"We're not in a position yet to get a medal."
Powell was similarly ambivalent about her side's performance, despite Britain creating the better of the chances and Kelly Smith missing a penalty.
"Yes, we played well in patches," she said. "It wasn't the complete performance by any stretch of the imagination. But we did a job, very resilient, worked hard. You saw the girls at the end. They were dead on their feet."
Powell was nevertheless "really pleased" with the outcome and the "electric" support of the unprecedented crowd.
"I must say the crowd were really inspiring tonight," she said. "I think they gave us a little bit of an edge, which was great for us.
"As a manager, certainly I've never experienced it. When I talk on the sidelines, the girls can usually hear me.
"Tonight was a good excuse for them to ignore me, which is what they tried to do...We actually spoke about it beforehand that 90 per cent of the crowd were there to support Team GB and, 'Go out there and enjoy it and they'll get behind you'."