Athletic Bilbao went down 3-1 away to Sparta Prague, as Oscar De Marcos' late goal was not enough to inspire a comeback.
The second half consolation from the 23-year-old was in vein, as earlier strikes from Tomas Zapotocny, Bekim Balaj and Josef Husbauer gave the Gambrinus Liga side the three points.
Marcelo Bielsa named a virtually full strength team for the trip to the Czech capital, but even their strongest XI could not stop the early pressure Vitezslav Lavicka's men were cultivating.
Gorka Iraizoz was forced into a pair of smart saves within the first 10 minutes – they then hit the post on 20 and the Rudi kept coming until they were 1-0 up midway through the half. Tomas Zapotocny struck a low shot from the edge of the area, that keeper Iraizoz led slide through his body.
The misery was not over for Leones' fans however. More relentless pressure from the Czech team saw Husbauer head back from the far post, in towards goal, where Balaj was there to double the lead.
And it got even worse for the San Mames side just after the interval. After a bright early start, the home side hit Bielsa's men on the break, with Xabi Castillo fouling Vaclav Kadlec inside the area. Husbauer converted the penalty, with Bilbao wondering, how has it come to this?
The introduction of Fernando Llorente gave the visitors' some more presence and impetus up front, and that paid off with 15 minutes remaining, as De Marcos pulled one back from Iker Muniain's pull back from the byline.
It was not enough though, to inspire a comback, and Bilbao go back to the Basque country still winless in the Europa League.
Sparta Prague 3-1 Athletic Bilbao
Scorers: Zapotocny 26 (SP), Balaj 42 (SP), Husbauer 56 (SP); De Marcos 73 (AB)
Sparta Prague: Vaclik; Zapotocny, Svejdik, Jarosik, Pamic; Holek, Husbauer; V. Kadlec, Matejovsky (Pavelka 79), Krejci (Skalak 72); Balaj
Athletic Bilbao: Gorka Iraizoz; Iraola, Gurpegi, Amorebieta, Castillo (Herrera 62); Iturraspe; Susaeta, Muniain, De Marcos, Ibai Gomez (Ismael Lopez 57); Aritz Aduriz Llorente (64)
Referee: Manuel De Sousa (POR)