Johan Voskamp scored two minutes into his Slask Wroclaw debut to give the Poles victory over Dundee United in their Europa League qualifier.
Johnny Russell and David Goodwillie both missed great chances as United matched the Polish top-flight's runners-up for much of the first leg.
United goalkeeper Dusan Pernis saved well from Cristian Diaz then, after the break, Amir Spahic.
But Dutch substitute Voskamp headed in from 14 yards after 76 minutes.
It means that Orest Lenczyk is half way to avenging the 7-2 aggregate defeat by United that led to his sacking during his first spell as Slask coach 31 years ago.
Striker Jon Daly had been drafted into United's central defence in the absence of the injured Garry Kenneth for a Tannadice outfit who have suffered the loss of several players to summer transfers.
That meant Goodwillie was up front on his own despite that leaving the Scotland striker cup-tied for sections of European competition and perhaps reducing transfer interest from the likes of Rangers.
Diaz, Slask's Argentine striker, provided the first goal threat with only eight minutes gone but pulled his shot from just inside the penalty box wide of the far post.
United ought to have taken the lead moments later when Russell did well to dispossess a defender and round goalkeeper Marian Kelemen only to knock his effort wide of the post from the penalty spot.
The home side responded and lively winger Marek Gancarczyk cut inside before smashing a drive just over the United crossbar from 18 yards.
Peter Houston's side should have scored on the break when Goodwillie beat his marker for pace, but Kelemen did well to get a hand to the ball and divert it for a corner when the striker delayed his shot until after his attempt to round the goalkeeper.
It was United goalkeeper Dusan Pernis' turn to produce a superb, diving save to turn a Diaz drive round the post, while Bosnian defender Spahic sent an effort just wide.
Slask started the second half with greater purpose and Spahic was denied by an excellent save from Pernis after the former Torpedo Moscow man headed for goal.
Slovenian midfielder Rok Elsner was next to threaten with a thunderbolt that flew just over the crossbar.
A cross from Paul Dixon almost deceived the Slask goalkeeper as it appeared to be heading for the far post, but Keleman pushed the ball clear and, from the corner, debutant Willo Flood's cross just evaded Goodwillie.
Voskamp was only on the field for two minutes of his debut when substitute Waldemar Sobota's mis-hit shot was diverted into the net off the head of the 26-year-old former Sparta Rotterdam striker.
United's problems could have deepened when experienced midfielder Scott Severin pulled up in the dying seconds with what appeared to be a hamstring injury.