Myanmar keeper Phyo Kyaw Zin was the man of the match against Vietnam and produced several key saves, before Tun Nay Lin scored a late winner for Kyi's side.
The result means Myanmar has advanced to the gold medal match at the SEA Games for the third time since 1993, although they have not lifted the title since their run of five victories ended in 1973.
"No matter who play … we are more confident for the final," Kyi said after the match.
"Not only the coaching group, but all the players."
Having dominated the match in terms of possession and territory, Vietnam coach Toshiya Miura was disappointed with the outcome.
"Maybe Myanmar was lucky, but we had at least five chances. But this is not just Vietnam's problem — every Asian country has the same problem,” Miura said.
Myanmar takes on Thailand – who beat Indonesia 5-0 in their semi-final – on Monday.