The action took a little while to heat up, as both teams tentatively sussed each other out.
Michael O’Neill’s side got the better of things though, taking the lead in the 15th minute when Dion Charles used the outside of his right boot to bend a beautiful pass to Isaac Price, who duly converted from inside the area.
That was the first goal that the visitors had conceded in this UNL campaign, and another nearly came quickly when a mis-hit Callum Marshall cross whistled narrowly over the bar.
The hosts did not have to wait long for a second though, as the referee played a terrific advantage when Charles was tugged to the ground in the box, but the ball fell to Price, who doubled his tally for the evening with a deflected strike that found the far corner.
Minutes later, it was 3-0, with Brodie Spencer letting rip with a fizzing strike from distance that rattled the post, but bounced onto goalkeeper Dimitar Mitov and over the line.
Bulgaria, unbeaten in nine internationals ahead of his clash, were shell-shocked. Perhaps that goes some way to explaining why they couldn’t pull one back before the break.
Kiril Despodov was presented with a penalty after Eoin Toal bundled over Martin Minchev in the box, but the spot-kick smashed the bar as he went for power over placement.
The Green and White Army meanwhile were far from done, and Charles nearly added a fourth after HT, before having another ruled out for offside.
It mattered not though, as Price wrapped up his hat-trick with a sensational strike from outside the box, superbly finding the far top corner with a bullet of a strike.
Not quite content with their night's work, Northern Ireland added a fifth through Josh Magennis, converting off the bar with a powerful strike after a lovely first touch.
As such, Northern Ireland boosted their hopes of promotion back to the second tier of the UNL by moving into top spot in Group 3, one point above previous leaders Belarus, whereas the visitors suffered their joint-heaviest defeat since October 2019.
Flashscore Man of the Match: Isaac Price (Northern Ireland)