Kimberly Yeo, 23, managed to send a 160-character SMS message in just 43.24 seconds.
It knocked more than 20 seconds off the official record of 67 seconds held by Briton James Trusler.
Guinness are still waiting to verify the new record set at a competition run by Singapore telephone company, SingTel.
The runner-up in the 125-competitor event on Sunday, Ashley Tan, 18, finished just 0.2 seconds behind Miss Yeo, reports local media.
Would-be record breakers all have to send the same message to ensure a level playing field.
It reads: "The razor-toothed piranhas of the genera Serrasalmus and Pygocentrus are the most ferocious freshwater fish in the world. In reality they seldom attack a human."
Competitors are not allowed to use spelling aids or a predictive text programme on their phone.
Ms Yeo, a business administration student who sends thousands of messages a month and won £8,000 in cash and other prizes, said she had been extremely nervous before the event.
"There are a lot of people, the contestants and everyone, so it's very pressurising," she told Channel News Asia.
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