Two lates goals gave Athletic Bilbao hope after a 3-2 defeat to Trabzonspor.
Late goals from Carlos Gurpegi and Asier Del Horno gave Athletic Bilbao renewed hope of progressing after a 3-2 defeat against Trabzonspor.
The Basque outfit found themselves two goals down midway through the first period when, after Javi Gonzalez had put through his own net following a mistake from Daniel Aranzubia on 26 minutes, Mehmet Yilmaz rifled home from the edge of the box to double the lead a minute later.
Things got even worse for Athletic when Gokdeniz Karadeniz made it three 20 minutes from time and their European campaign looked set for a premature exit.
However, midfielder Gurgepi dragged his side back into the tie with a strike on 73 and seven minutes later Del Horno thumped home a superb header from a Yeste free-kick.
Bilbao coach Ernesto Valverde will now hope his troops can complete the job at the San Mames.
Villarreal continued their excellent European form with a 2-1 away success against Hammarby.
The Yellow Submarines raced into a two goal lead inside 23 minutes after strikes from Antonio Guayre and Gonzalo Rodriguez.
Guayre opened the scoring on 12 minutes when he cut in off the left flank and drifted past his defender before driving home an accurate low shot across the goalkeeper.
Gonzalez added a second eleven minutes later, but the Swedes reduced the arrears almost immediately when Bjorn Runstrom got on the end of a long ball to beat Carlos Reina.
The hosts went close to equalising in the second half when they hit the bar, but Villarreal will now fancy their chances of moving through.
Sevilla begun their first European adventure with a comfortable 2-0 win over Portuguese side CD Nacional.
Brazilian midfielder Julio Baptista opebned the scoring just past the half hour mark when he knocked home after good work from Dario Silva.
They gave themselves breathing space for the return leg ten minutes from time when Sergio Ramos headed home after a long ball wasn't properly cleared.
David Generelo netted a late winner to hand Real Zaragoza a slender advantage over Sigma Olomouc.
The midfielder raced on to David Villa's back-heel to drill home a left-footed effort that ensures the Aragon-based outfit head to Czech Republic with an advantage.
Match summaries:
Hammarby 1-2 Villarreal
Real Zaragoza 1-0 Olomouc
Sevilla 2-0 Nacional
Trabzonspor 3-2 Athletic Bilbao
