The 20-year-old was disappointed with her 100 swim at the Brisbane Aquatic Centre but glad to top a quality field.
"At the end of the day, trials is just to make it on the team, so I'm pretty stoked with that," O'Callaghan said poolside. "But you know there's that little extra that you want."
A fixture in Australia's 100-meter freestyle relay teams since the 2008 Beijing Olympics, Cate Campbell was devastated after failing to qualify for the final. She has an uphill battle to win a 50-meter freestyle berth and secure a fifth Games appearance.
Her younger sister Bronte, however, finished fourth in the 100-meter final to nab a spot on the relay team along with Meg Harris (third) and 18-year-old Olivia Wunsch (fifth).
Bronte Campbell struggled to hold back tears as she paid tribute to 32-year-old Cate, who won two relay golds at Tokyo and the individual 100-meter bronze.
"I felt devastated for my sister this morning," she said. "But she is absolutely incredible. I mean, she held this individual spot in the 100 freestyle for 11 years. I think that's got to be a record in Australia."
