I have been looking for bigger comeback than PSG vs Barcelona in 2017 i.e La Remontada in which Barca beat PSG in second leg. Artmedia Bratislava vs Celtic was close as they lost 5-0 in first leg but Celtic could get only 4. I have found couple of examples but all were 4 goal Real Madrid vs Borussia Mönchengladbach, 1985-86 UEFA Cup Partizan Belgrade vs QPR, 1984-85 UEFA Cup Leixões SC vs FC La Chaux-de-Fonds,1961/62 UEFA Cup CONMEBOL 1995 cup...
Originally asked by backl on Stack Exchange (sports) (CC BY-SA 4.0).