Niamh Clarke-Willis, who can see the Olympic Park from her home in the east London borough of Hackney, stepped out into the infield of the £500 million stadium with London 2012 chairman Seb Coe.
Together they pressed a blue button that opened a net and sent balloons swirling above the 40,000-strong crowd, who had snapped up the available tickets in a mere 20 minutes, as a light show filled the sky on a chilly night.
The lucky youngster was chosen to do the honours at a special test event celebrating 2,012 hours to go until the Games begin on July 27.
Paralympic gold medal-winning archer Danielle Brown had earlier shot arrows at two spinning targets to select a name from 100 pre-selected eight to 14-year-old girls and boys.
In fact the stadium had already been open for business for a day, with Saturday's event coming at the end of the British Universities and Colleges (BUCS) outdoor championships.
In what may not be the most auspicious omen for Team GB, who hope to enjoy a British gold rush, the first athlete to win a race on the gleaming new track on Friday evening was an Irish hurdler.
"I feel like I've just won a major championships or something," declared Justine Kinney, a 24-year-old psychology masters student at Loughborough University - alma mater of London 2012 chairman Seb Coe.
"It feels amazing to know that all these world class athletes are going to be running down this track in just a few months," she said after winning her 400 metres heat on Friday.
"The track feels amazing, it feels like you could fly down it," she added.
Some world-class athletes were already in attendance on Saturday, with retired five-times rowing gold medallist Steve Redgrave and swimmer Mark Foster among celebrities involved in the proceedings.
Other athletes included Eilish McColgan, daughter of Olympic 1988 10,000m silver medallist Liz, in the 1,500m.
British Olympic track hopeful Perri Shakes-Drayton and pole vaulter Holly Bleasdale were on track as was James Ellington, a sprinter who put himself up for auction on eBay to secure sponsorship and who won a UK Athletics 100m race.
"This crowd will not only be starting their Olympic journey just weeks ahead of the Games, they will also play a vital role in helping us test the venue and earn our licence to operate the Stadium," Coe, whose presence meant he missed watching his beloved Chelsea win the FA Cup at Wembley, had said beforehand.
They were also excited about being part of history.
"I walked around anonymously last night and I was just listening to the excitement of the people who were walking in, it was a bit like watching my kids on the first day they woke up to find snow in the back garden," Coe said.
The stadium, at the centre of the Olympic Park in a formerly rundown part of east London, will go into lockdown from May 12 as organisers put the final touches to the facility.