Striker Sone Aluko struck an 81st-minute winner as Hull City beat Trencin 2-1 at the KC Stadium to book their place in the Europa League playoffs.
Aluko, who had earlier replaced the misfiring Long, volleyed Thomas Ince’s cross into the roof of the net with nine minutes remaining.
Steve Bruce’s side were expected to progress into the fourth and final qualifying round, despite being held to a goalless draw in last week’s first leg in Zilina.
However, the Slovakians sprung a surprise for the Premier League outfit by bagging a key away goal after just two minutes.
It was Tomas Malec who opened the scoring, rifling past goalkeeper Allan McGregor from 14 yards to give the Tigers a mountain to climb.
The hosts responded well and should have restored parity in the 25th minute, as Shane Long spurned two good opportunities in front of goal to level matters.
Ahmed Elmohamady was on hand to spare the Irishman’s blushes, however, as the midfielder evaded his marker to nod home a Robbie Brady cross two minutes later.
City started the second half as haphazardly as they began the first and lightning nearly struck twice when Haris Hajradinovic saw a deflected effort glide agonisingly wide.
Bruce opted to replace Brady with Liam Rosenior moments later, and the change nearly yielded instant rewards as the midfielder’s half-volley drifted narrowly past the post.
Trencin might have spoiled Hull’s party in the dying stages when they were awarded a free kick in a good position, but Jakub Holubek’s effort marginally cleared the bar to ensure City’s progression.