Just two days after 30-year old David Carry became the oldest Brit to add his name to the roster, 16-year-old O’Connor clocked a personal best of 1:08.04 to capture gold and clinch her Olympic berth.
The British Gas ITC Bath swimmer underlined her potential by reaching the 200m individual medley semi-finals at last year’s World Championships in Shanghai.
But after missing out on an Olympic spot in the 200m IM, O’Connor wasn’t to be denied in the 100m breaststroke, having sacrificed her school prom to compete on Friday evening.
She set a 1.26 second personal best to qualify fastest from this morning’s heats before leading the final from gun to wall to seal victory in 1.08.04.
"I’m so shocked," said O’Connor. "I found it so hard to deal with missing out in March but I had to get back in and do the hard work.
“At one point I never saw myself going to London but I’ve given everything in training. I’ve focused so much since then and now I’m going to the Olympic Games. It is just unbelievable."
Rebecca Adlington may have already confirmed her Olympic selection but the double Olympic champion was in dominant form as she claimed gold in her favourite 800m freestyle.
Competing in her last event before London 2012, the Nova Centurion swimmer, who also lifted 200m freestyle gold on the opening day in Sheffield, proved too strong for her national rivals as she stormed home in 8:19.03.
Stephanie Proud (Chester-le-Street) also clinched the qualification time for her first Olympics with a golden performance in the 200m backstroke.
Having clocked his first Olympic qualification time in the 200m backstroke 24 hours before, Chris Walker-Hebborn secured his second in as many days with gold in the 100m backstroke.
The Bath swimmer took the race out confidently before coming home to touch in a lifetime best 54.26seconds - 0.14s under the Olympic standard.