Braga entered matchday four as one of just three teams to have won each of their opening three league phase fixtures, and they were yet to concede a goal in the competition ahead of their first-ever contest with Genk.
A tentative start from the hosts allowed the Belgian side to threaten an upset, but Yira Sor’s misplaced pass - with Patrik Hrosovsky poised to break clear - saw a promising counter-attack go to waste.
Braga’s growing dominance in possession eventually told on the half-hour mark, as Rodrigo Zalazar latched onto a poor-headed clearance, drove forward, and dispatched a pinpoint finish into the bottom-left corner from the edge of the area.
Braga appeared comfortable as half-time neared, but their night was about to unravel as their perfect record was undone in the final seconds of the first half when Daan Heymans’ glancing header stunned the Arsenalistas, just moments after his initial effort had been deflected behind for a corner.
The worst, however, was yet to come for Carlos Vicens’ men in what transpired to be an action-packed second period.
And when they cheaply lost possession three minutes after the restart, Sor put Genk in front to make amends for his earlier error, breaking forward and checking onto his right foot before thumping the ball past Lukas Hornicek off the underside of the bar.
Despite Braga’s dominance in possession, Thorsten Fink’s side remained brutally ruthless, and the Portuguese team were again put to the sword when Heymaans’ cutback was emphatically swept in by Oh Hyeon-Gyu on 59 minutes to extend Genk’s shock lead.
In a rollercoaster second half, Braga hit back when Zalazar headed in his second of the evening, but defiant Genk responded immediately from kick-off as substitute Yaimar Medina curled into the far corner from 18 yards, to quash hopes of a Braga fightback.
A chaotic finale ensued when Fran Navarro bundled in to give the hosts a lifeline with less than five minutes remaining, but Genk held firm as Braga desperately pressed for an equaliser.
The result will no doubt galvanise Genk’s European campaign, having now registered back-to-back wins in the competition. Meanwhile, shell-shocked Braga face a testing run-in with three of their remaining four fixtures to be played away from home.
Flashscore Man of the Match: Rodrigo Zalazar (Braga)