During her training for the women's 200m individual medley at the world championships, South Korean swimmer Kim Seo-yeong was so confident that she felt she could break her own national record.

And that confidence never waned in the warmup at Nambu University Municipal Aquatics Center in Gwangju on Monday. And the 25-year-old carried that self-assurance into the pool in the final.

Kim left the water wondering where it had gone.

She finished sixth among eight finalists at the FINA World Championships with a time of 2:10.12. Katinka Hosszu of Hungary won her fourth straight gold in 2:07.53.

Kim's national record time is 2:08.34. That would have placed her in second place Monday, as Ye Shiwen of China took the silver in 2:08.60. But in three races in Gwangju, covering the preliminary, semifinals and final, Kim never once broke the 2:10 mark.

"My objective was to have a race without having any regrets," Kim said. "I am disappointed with my time today. I thought I did better today than yesterday (in the preliminary and semis) but I am still not pleased with this."

Kim's next event will come on the final day of these championships, on Sunday, the 400m IM.

"Rather than feeling down about what happened tonight, I will try to forget about this right away," she said. "I have to start concentrating on the 400m IM."

Kim has gotten noticeably bigger around the shoulders in recent months, and she said she has become much stronger. But she admitted the added bulk has cost her an ability to handle fine points of her race management, without getting into specifics.

This was Kim's second straight appearance in the 200m IM final.

In 2017, she finished sixth as the first South Korea to make the world championships final in a medley event.

Kim was hoping to become the first South Korean female swimmer to win a world championships medal. (Yonhap)