West Ham's hopes of reaching the quarter-finals of the Europa League hang in the balance after they fell to a narrow defeat at Sevilla in the first leg of their last-16 tie.
Munir El Haddadi scored the game's only goal for the six-time winners, sweeping in superbly from Marcos Acuna's free-kick on the hour mark.
Until that point David Moyes' West Ham side had more than held their own in their first knockout tie in a major European competition since 1981.
Nikola Vlasic headed an early opportunity straight at Sevilla goalkeeper Yassine Bounou, Michail Antonio then missing his kick with the follow up from close range.