The Singapore men's 4x100m freestyle relay team had looked set to retain their SEA Games title after finishing first in 3min 17.19sec, ahead of Malaysia (3:20.13) and hosts Vietnam (3:21.81) at the My Dinh Water Sports Palace on Saturday (May 14).
But midway through their post-race interviews, the Republic's quartet of Joseph Schooling, Mikkel Lee, Quah Zheng Wen and Jonathan Tan received a rude shock when they were told that they had been disqualified. They were then ushered away.
Malaysia and the Philippines were also disqualified, leaving Vietnam (3:21.810) to take the gold, with Indonesia (3:24.090) and Thailand (3:24.280) completing the podium under the official results.
Swimming's national head coach Gary Tan said: ''Kudos to the boys, no fault of anybody's.
''I think this is something that happens in a competitive environment and it just goes to show our boys are hungry to win that medal. We'll turn something that was bad today into something good hopefully in the next few days.
''It's based off a technicality, it's very tough to make that protest even though we were trying to find a reason and wanted to make sure that this was not an issue of a technical error.
''I don't want to put it in a bad way, but there have been a lot of problems with what's been happening technically on the ground here. We work with whatever the circumstance is and we work with it.''
At the last SEA Games in the Philippines in 2019, Singapore had won the men's 4x100m free relay in 3:16.82.
This was Schooling's first race of the Hanoi Games. He will also be defending his 100m butterfly title.