The early goal proved enough as Belarus held on for three points that significantly strengthened their position in a tightly contested group. UEFA's official results confirm the 1-0 victory.
Shumanskiy strikes inside the opening minute
Belarus made a sensational start when Artem Shumanskiy found the net in the first minute.
The goal came almost immediately after kick-off and gave Belarus the perfect platform to control the match against a Finland side that had previously shown strong form in the group.
Finland were unable to find an equaliser despite having plenty of the second-half possession and introducing several attacking players from the bench.
Finland unable to break Belarus down
Finland pushed forward after falling behind but found Belarus difficult to penetrate.
The hosts defended their narrow advantage effectively and goalkeeper Zakhari Volkov made an important contribution as Belarus protected their lead.
Finland made a number of changes after the interval, including the introduction of Joel Pohjanpalo, but the visitors could not find a way past the Belarus defence.
Belarus hold on for important three points
The final whistle confirmed a 1-0 victory for Belarus, their second consecutive win after the emphatic 4-0 victory over San Marino on 3 October.
Belarus 1-0 Finland
• Belarus: Artem Shumanskiy 1'
• Finland: No goals
Belarus strengthen their position in Group C1
The victory gives Belarus an important boost in Nations League Group C1.
Before Tuesday's match, Belarus had beaten San Marino 4-0, drawn 0-0 with Finland and lost 2-0 to Albania. The latest victory means they have now collected seven points from four matches.
Finland, meanwhile, suffered their first defeat of the group phase after previously beating San Marino and Albania and drawing with Belarus.
Crucial final fixtures ahead
Belarus will now turn their attention to their final two Group C1 fixtures in November.
They travel to face San Marino on 12 November before hosting Albania on 15 November.
With the group still finely balanced, Belarus' narrow victory over Finland could prove crucial in determining the final promotion and qualification picture.