Taking a 1-0 lead from the first leg to Wales, Niederkorn were pegged back to level terms as soon as the second minute in their away match against Cardiff Metropolitan University when Jordan Lam scored for the home team. And they were facing elimination when the Cardiff part-timers took a 2-0 lead in the 67th minute through a penalty converted by Dylan Rees.
New signing from Hamm Benfica, Issa Bah, started for Niederkorn on the day before his 17th birthday. But it was 23-year-old Belgian Mayron de Almeida who struck the vital goal in the 72nd minute and Niederkorn then held out to go through on the away goals rule.
The Luxembourg team now faces a trip to Ireland to play Cork City on 11 July in the first round proper of qualifying. The return leg is scheduled for 18 July.
If they get through over two legs against Cork, Niederkorn could again face Rangers, the team they famously dumped out of the competition in 2017. Captain Sebastien Thill has said the players are pumped up to try and get a rematch with the team from Glasgow, now managed by Liverpool legend Steven Gerrard.