FULL-TIME: Petrolul Ploiesti 2 Swans 1
The Swans booked their place in the Europa League Group Stage despite a 2-1 defeat to Romanian outfit Petrolul Ploiesti.
The hosts had taken the lead at the Ilie Oana, with substitute Abel Camara firing them ahead in the 73rd minute, only for fellow replacement Roland Lamah to level 60 seconds later.
But Petrolul, backed by a vocal home crowd, weren't to be denied victory as Hamza Younes headed home with seven minutes remaining to claim victory.
Leon Britton, captain for the night in Ashley Williams' absence, was given his marching orders in the latter stages for receiving a second yellow card.
Despite the defeat, the Swans progressed into the Group Stages 6-3 on aggregate.
Michael Laudrup made five changes to his starting XI.
Rory Donnelly made his first start for the Swans - who led 5-1 from the first leg - while Alejandro Pozuelo provided support from out wide as he was included in the XI.
Leon Britton was named skipper, as Ashley Williams didn't travel to Romania, while Jordi Amat and Gerhard Tremmel were the other changes from the side that lost 1-0 at Tottenham Hotspur last time out.
Petrolul Ploiesti: Mircea Bornescu, Jean Sony Alcenat, Geraldo Alves, Sony Mustivar (capt, Romario, 66), Damien Boudjemaa, Hamza Younes, Ovidiu Hoban, Njongo Priso, Guilherme, Pablo De Lucas (Filipe Teixeira, ht), Ferebory Dore (Abel Camara, ht).
Subs not used: Pecanha, Alexandru Benga, Sebastian Achim.
Swans: Gerhard Tremmel, Angel Rangel, Chico Flores, Jordi Amat, Ben Davies, Leon Britton (capt), Jonathan de Guzman (Ki Sung-Yueng, 61), Michu (Jose Canas, 77), Alejandro Pozuelo, Pablo Hernandez (Roland Lamah, 67), Rory Donnelly.
Subs not used: Michel Vorm, Jazz Richards, Garry Monk, Wayne Routledge.
The Swans started cautiously against the hosts, who were backed a vocal home crowd.
Neither side threatened until Alejandro Pozuelo broke down the right but his low cross to Rory Donnelly was intercepted before the striker could meet it.
Michu then sent Donnelly racing towards goal with a neat volleyed pass, but the young forward's shot dragged wide.
Michael Laudrup made a change on the hour, with Ki Sung-Yueng replacing Jonathan de Guzman.
It was Ki's pass which help set up the next chance, with the ball eventually falling to the feet of Pablo Hernandez, but his chip was collected easily by Mircea Bornescu.
Hernandez then drove an effort over the crossbar before Donnelly found the back of the net, only for his strike to be ruled out for handball.
Ovidiu Hoban then dragged an effort wide for the hosts, who then took the lead in the 73rd minute.
As the Swans defence looked to catch the hosts offside, sub Abel Camara took advantage as he controlled before firing past Tremmel.
But the lead didn't last long as Roland Lamah - on for Hernandez in the 67th minute - struck past Bornescu via the inside of the post from a Pozuelo cross just a minute later.
The hosts, though, weren't on level terms for long as Hamza Younes headed home from five yards out in the 83rd minute.
The drama didn't end there, however, as Britton was sent off after receiving a second booking with minutes remaining.
It means he will now miss the first match of the Group Stage, with the Swans finding out their opponents on Friday afternoon.