O'Keeffe was challenged throughout by veteran triathlon competitor Rob Gemmell, snapping at her heels.
"I could feel him behind me a few times, got a few nips.
"But it's good to have someone there to push you."
Gemmell, who opted to race in a wetsuit, was also happy with his 34m 4s effort.
"The river's really clear. I could see her feet well enough to stay on them.
"But she was too quick there at the end - took off on me."
It was a good chance for Wanganui's two latest national representatives to have a dip as Elena Forlong and Shannon Schimanksi, chosen last week for April's Australian Age Group Championships, took part.
Forlong finished third overall in the 3km race.
Schimanski combined with Mia Gemmell to win the team's race in 38m 1s, followed by Team Kakashi and the Pink Llamas.
"I'm not really a freestyler, just did it for fun," Schimanski said.
She is eager for her first opportunity to represent New Zealand, having experienced competing in Australia previously for her club at the Victoria State Championships last summer.
"I didn't think we were going to make it. Then after training Elena's dad told us and it was really exciting."
Unlike last year, the 1km course competitors started a little earlier than the stronger swimmers in the 3km race, which meant Briley Zimmerman was the first person to climb out of the water, winning the short-course race in 14m 5s.
"Got the national triathlon champs coming up, so it's training," she said.
Second overall was Michael Hiroti in 15m 32s, followed by Blake Hogan just two seconds later.
The next event for the club is the Kids Triathlon at the Splash Centre and around Springvale Park this Sunday at 10am.