Both divers scored 237.57 points, which was 8.16 points higher than Singapore's Ashlee Tan Yi Xuan and Fong Kay Yian. Malaysian divers Ng Yan Yee and Ong Ker Ying continued to dominate the competition, winning gold with a total score of 276.30 points.
"We had targeted a bronze and were not expecting to perform so well," Mai said after the competition at My Dinh Aquatic Center in Hanoi.
Mai had won bronze medals in three previous editions of SEA Games held in 2015, 2017 and 2019. She also won bronze in the women's single 1m springboard event Sunday.
"I am proud to bring home a silver medal today. This has been something I've been looking forward to for a long time."
Before the women's synchronized diving final, six athletes from four teams from Vietnam, Thailand, Singapore and Malaysia competed in the men's singles 1m springboard final.
The discipline not being a strong event for the home team, Phuong The Anh and Nguyen Tung Duong achieved the lowest scores of 248.25 points and 230.10 points, respectively.
Duong, once ranked fourth at the SEA Games 30, even got 0 points for making a mistake of letting his back make contact with the water when landing in his final dive.
Malaysia's Ooi Tze Liang achieved 377.70 points and won the gold, ahead of Singapore's Avvir Pac Lun Tham (286.40 points) and Malaysia's Betrand Rhodict (284.90 points).
The diving contest will be held for another two days with the women's singles 1m synchronized diving and men's doubles 10m platform diving on Tuesday; and the men's singles 3m springboard diving and women's doubles 10m platform diving the following day.
Synchronized diving, diving and swimming are three aquatic sports disciplines in this SEA Games edition.
Seven teams from Malaysia, Thailand, Cambodia, Indonesia, Singapore, the Philippines, and Vietnam are competing in eight events.
The Vietnamese diving team has nine athletes competing in the event.
After two days, local divers have brought home three medals. Besides Mai's bronze in singles and silver in doubles, Duong and Anh pocketed a silver medal in men's doubles 3m springboard on Sunday.