Sevilla, who have won the competition the last two years, will be confident returning home, although their hopes were dented slightly when Steven N'Zonzi was sent off late on for two yellow cards.
Chances were few and far between in the first half at St Jakob Park, with Marc Janko heading wide the clearest opening after just six minutes.
Birkir Bjarnason then blazed over for the hosts not long after the restart before Sevilla began to up the tempo and chase an away goal.
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The return leg takes place in a week's time at the Estadio Ramon Sanchez Pizjuan.