Iker Muniain scored the winner in the 42nd minute after an assist by Iñaki Williams. The goal had to be confirmed by video review as it appeared Williams controlled the ball with his arm before making the low cross for Muniain’s close-range shot.
The second leg will be on March 5 at Granada, which is trying to reach its first Copa final in more than six decades.
“We could have scored more goals,” Athletic coach Gaizka Garitano said. “But even if we had won 2-0, it still wouldn’t