Kunlavut Vitidsarn becomes the new world No.1 after reaching the final of the US$1 million BWF Singapore Open on Saturday.
Second seed Kunlavut booked his berth in the men's singles final after beating Lin Chun-yi of Taiwan 21-11, 25-23 at the Singapore Indoor Stadium.
The 24-year-old is set to officially become the new top-ranked men's player when the latest world rankings are released by the World Badminton Federation (BWF) on Tuesday, replacing China's Shi Yuqi.
Kunlavut is only the third Thai player to become world No.1 after mixed doubles pair Dechapol Puavaranukroh and Sapsiree Taerattanachai in 2021.
Kunlavut, who is chasing his third World Tour crown this week, will face China's Lu Guangzu or France's Christo Popov in the Super 750 final.
Kunlavut has won the Indonesia Masters and the Thailand Open this year -- both Super 500 events. He also claimed his maiden Asian crown last month.
Earlier, Dechapol and Supissara Paewsampran also reached the mixed doubles final.
The duo continued the pursuit of their third title of the year as they defeated Ye Hong-wei and Nicole Gonzales Chan of Taiwan 21-12, 21-12.
A day after knocking out top seeds Goh Soon Huat and Shevon Jemie Lai of Malaysia, the Thai duo proved too strong for the unseeded Taiwanese, winning their semi-final in just 32 minutes.
Dechapol and Supissara will face second seeds Tang Chun Man and Tse Ying Suet of Hong Kong in Sunday's decider.
The Thais won the Malaysia Open and the Thailand Masters earlier in the season.
The women's singles final will be an all-Chinese clash between Wang Zhiyi and Chen Yufei.
Second seed Wang edged past fourth seed Akane Yamaguchi of Japan 21-12, 12-21, 21-17 while fifth seed Chen overcame third seeded compatriot Han Yue 12-21, 21-15, 21-12.