Together with Jonathan Chong, the three did well enough to place Singapore third out of 14 competing countries.
"The sport is still very new in Singapore," said Jonathan Chong, president of the Apnea Association of Singapore (AAS).
"We did a lot better than we had expected, considering that the field was a very strong one."
The AAS was founded only this year. While it does not have National Sport Association (NSA) status under Sport Singapore, it is an affiliate of the Singapore Underwater Federation, the NSA that promotes diving and snorkelling.
Chong estimates there are about 300 people here who freedive recreationally while only a fraction are regular and elite athletes.
The local fraternity is hoping to capitalise on the momentum of the championship to introduce more people here to the sport - but also clear up misconceptions about it.
For starters, training to be a freediver does not simply involve holding one's breath - even if top local men like Chong can hold their breath underwater for more than six minutes.
Said the 28-year-old, who works in business development: "There are quite a lot of things to train for.
"On top of basic fitness, we train for (better body) tolerance of high carbon dioxide and low oxygen levels. We also do technique work and mental skills."
Chong and top freedivers here, for instance, train in and out of the pool up to five times a week.
Said Ooi, a 26-year-old veterinarian: "Very few know what freediving is, or understand the emotions and experience of freediving.
"Most people think it's just holding your breath, and a lot think that it's dangerous.
"But it's like driving a car or rock climbing. If you don't have the right safety measures in place or have no idea what you're doing, then those are dangerous too."
The sport has a low barrier to entry - a nose clip and any scuba diving mask are all one needs - and also offers benefits for athletes in other sports, added Chong.
He said: "The benefits of apnea are well documented in altitude training and its benefits cross into other sports.
"We hope to be able to go onto bigger events like the world championships and take on Asian powerhouses like Japan and Israel. We're already the top in South-east Asia - the next target is to go bigger."