The playoff match was decided in a single meeting, due to the prevailing pandemic.
And with only one match, it is important to avoid mistakes.
Unfortunately, for Northern Ireland, it started badly, George Saville chose to nod home, Slovakia's Juraj Kucka was instead completely free and was able to put in 1-0 already after 17 minutes of play.
The result almost stood the test of time, but with three minutes left, Paddy McNair cut forward on the right wing, sending in the ball which was then supported by Milan Skriniar.
Extension awaited in Belfast.
Former Manchester United defender Johnny Evans was unhappy with a ball drop.
Michal Duris was able to put in 2-1 at the first post, which was enough for European Championship advancement.
Slovakia will now meet Sweden on June 19 in Dublin, unless the European Championship program is repeated once more.