Amanda Lim was planted at the side of the pool, searching for family and friends in the crowd at Kuala Lumpur's National Aquatic Centre.
When she spotted them, she threw a soft toy of Rimau - the SEA Games mascot - towards them, but inadvertently failed to spot a young fan who had run down the stands to greet the Singapore swimmer.
But once she was alerted about the matter, the 24-year-old, who had won the 50m freestyle on Saturday, turned to social media for help to find the girl.
She put up a Facebook post on Monday evening and it went viral. And she managed to get in touch with the fan, eight-year-old Caitlin Chan, yesterday morning.
"It must be all the elation I was feeling that somehow clouded me from seeing anyone else other than my family from the crowd," Lim wrote.
In her post, she apologised to Caitlin for not noticing her, and asked netizens to help find the girl so she could send a Rimau to her "as a gesture of appreciation and apology for not seeing her that night".
She updated the post yesterday, saying she had identified Caitlin. "I will be doing my due diligence once I get back from my holiday!"
Lim told The Straits Times from the Maldives where she is now on vacation: "Within an hour after posting, I found the girl.
"It turns out that she is being coached by two of my friends at an international school, Siow Yiting (former Malaysian breaststroke specialist) and Eileen Leung (former Malaysian freestyle swimmer), so they texted me and gave me her mother's contact."
Caitlin's mother Weng Shin-yi, 42, told ST that it was "heart-warming" that a champion like Lim would take the effort to reach out to a young fan like this.
"I think it's just a sweet thing. She (Lim) didn't have to do this, but she decided to reach out to a little girl and make her day," she said.
The family of Singaporeans are based in KL as Caitlin's father works in the food industry there.
They had gone to watch the SEA Games swimming competition as Caitlin is a keen swimmer and aspires to be successful like Lim when she grows up, said Weng.
"Caitlin said she wanted to go down to say 'hi' to Amanda at the end, so I told her to go ahead.
"The steps were quite narrow, so she took quite a while to get to the bottom. We really thought nothing of the incident."
Weng was surprised when Lim posted the matter on Facebook, and social media did the rest.
Lim then texted Weng, who said: "She was very nice. I told her no need to explain herself, as she had just won a race and everyone was happy."
Caitlin, who her mother said was thrilled, recorded a video message to the swimmer. Lim added: "It was so sweet. She is so well-spoken.
"I hope this whole thing can inspire her, and that I can meet her."