ŠK Slovan Bratislava and HJK Helsinki provided the shocks − the latter defeating FC Schalke 04, UEFA Champions League semi-finalists last term − on a mixed night of play-off action for some of Europe's biggest names.
Paris Saint-Germain FC, Tottenham Hotspur FC and S.S. Lazio all but booked themselves a UEFA Europa League group stage berth courtesy of comprehensive first-leg wins. Roma, though, have it all to do after succumbing to Martin Dobrotka's 80th-minute goal for Slovan on Luis Enrique's competitive debut as Giallorossi coach.
In what is shaping up to be a memorable European campaign for HJK, Teemu Pukki scored twice in a 2-0 victory over Schalke to move within 90 minutes of becoming the first Finnish team this millennium to qualify for the group stage of a UEFA club competition. HJK registered a record-breaking 10-0 success against Bangor City FC in UEFA Champions League qualifying last month.
Shamrock Rovers FC (1-1 v FK Partizan), FC Zestafoni (3-3 v Club Brugge KV) and FC Nordsjælland (0-0 v Sporting Clube de Portugal) also shone at home against fancied opponents. Hannover 96, meanwhile, go into next week's second leg against two-time UEFA Cup winners Sevilla FC with a 2-1 lead thanks to Jan Schlaudraff's first-half double in Germany.
Elsewhere, Jérémy Menez rounded off the scoring in PSG's handsome 4-0 triumph in Luxembourg against FC Differdange 03 while Djibril Cissé began his Lazio career with two goals as the Biancocelesti brushed FK Rabotnicki aside 6-0 at the Stadio Olimpico. Cissé's former employers Panathinaikos FC fared less well, losing 3-0 to a Dor Mikha-inspired Maccabi Tel-Aviv FC.
Runners-up in the final three months ago, SC Braga were held 0-0 at home by BSC Young Boys, though 2010 winners Club Atlético de Madrid fared better as two goals in five second-half minutes from Elías secured a 2-0 triumph over ten-man Vitória SC.
The side Atlético overcame in that final, Fulham FC, have one foot in the group stage thanks to a 3-0 defeat of FC Dnipro Dnipropetrovsk at Craven Cottage. London rivals Tottenham went two better with a 5-0 success at British rivals Heart of Midlothian FC.
With the final taking place in Bucharest, the five Romanian clubs went into their ties dreaming of a date in the May showpiece. SC Vaslui, FC Steaua Bucureşti and FC Rapid Bucureşti did their prospects the power of good with two-goal wins but FC Dinamo Bucureşti and CS Gaz Metan Mediaş have it all to do following defeats by FC Vorksla Poltava (2-1) and FK Austria Wien (3-1).
The results of all 38 of Thursday's first legs can be found in the UEFA.com MatchCentre.