Alaves have one foot in the quarter-finals of the Copa del Rey following a 3-1 victory over Formentera at the Estadio Municipal on Wednesday evening.
Both teams had early chances once the whistle blew, with Ermedin Demirovic coming close for Alaves with a shot from the centre of the box, while his opponent Fernando Quesada had his attempt blocked a few minutes later.
The visitors began taking control of the ball, and Guillermo Maripan almost broke the deadlock before the half-hour mark with a header towards the left corner, but his effort went wide.
Demirovic had better luck a few minutes later when his header nestled into the back of the net after he latched on to Victor Lopez's cross.
Ruben Sobrino had an opportunity to double Alaves's lead before the half-time break, but his right-footed attempt from outside of the box was saved.
At the other end, Gabri almost sneaked in an equaliser for Formentera when he got on the end of a cross and tried to guide the ball past the goalkeeper, but the post denied him.
The hosts eventually levelled up proceedings in the second half when Omar Alvarez's corner kick found the head of Javi Rosa, who nodded it home from six yards, but their revival was short-lived when Demirovic regained the lead for Alaves.
Munir El Haddadi wrapped up the match for the visitors when his low shot slid past the keeper and into the bottom left corner following a swift counter-attack.
Formentera (4-1-4-1): Contreras; Rosa, Quico, San Jose Fernandez, Bonilla (Crespo 68'); Alvarez (Vinicius 74'); Gabri (Ojeda 68'), Muniz Cegarra, Quesada, Riera; Antonio Curieal
Alaves (4-3-2-1): Sivera; Dieguez Grande, Ely, Maripan, Lopez; Torres, Medran (Garcia 65'), Wakaso; Ibai (Munir 74'), Sobrino; Demirovic (Aguirregabiria 78')
