At the Traveler's Hotel in Subic, the 20-year-old scored 6.5 points in the men's group rapid chess competition, level on points with Nguyen Ngoc Truong Son, who won two gold and one bronze the last time chess was contested at the SEA Games in 2013.
However, he edged ahead of the Vietnamese thanks to a better tiebreaker score, while two-time Vietnamese Chess Championships winner Nguyen Anh Khoi took home bronze.
Bravo!!! Kontinjen Malaysia
— #TeamMALAYSIA ?? (@AtletMalaysia) December 3, 2019
Emas Yang Ke 12 Dari Atlet Chess ??♟Yeoh Li Tian Kategori Rapid Men’s #KontinjenMALAYSIA pic.twitter.com/HrwlmBkUa4
"I did not expect to win the gold medal, as I only targeted to win silver or bronze.
"I knew I had a chance but I did not expect I would get the gold medal in my first [SEA Games] appearance.
"It was very difficult because Vietnamese players won many games, so I also need to win a lot of games," he told Astro Arena.
Yeoh was the first Malaysian to compete at the 2017 FIDE World Cup, where he was knocked out by former world champion Viswanathan Anand in the first round.
Malaysia's previous best SEA Games achievement in chess was bronze in 2003, 2011 and 2013, while they went home empty-handed in 2005.
In the women's category, Singapore's Gong Qianyun (gold) and Indonesia's Ummi Fisabilillah (silver) and Irine Sukandar (bronze) made it to the podium as Malaysia's Tan Li Ting missed out.
Watch Astro Arena's live coverage of the 2019 SEA Games here!