After heroics at Old Trafford in midweek, Vincenzo Montella and his Sevilla faced a challenge at a hostile Butarque.
For the first 15 minutes or so the momentum was clearly on the side of the visitors, dominating the early stages of the game but failing to convert their chances.
Then, on the stroke of half-time, Leganes got a goal to put them ahead with Unai Bustinza’s looping header from the far post left Sergio Rico with no chance.
In the second half, Diego Rico burst down the wing and crossed into the box to set up Javi Eraso in space to double Leganes’ lead.
Pablo Sarabia’s frustration got the better of him, seeing him twice booked for needlessly kicking out with no plan to get the ball and forcing his side to see the game out with ten men.
Miguel Layun added a late consolation strike with a powerful finish leaving Ivan Cuellar sprawling, but it was too little too late for the visitors.
The defeat for Sevilla sees them now sit way off Valencia in the final Champions League places, whilst Leganes have all-but assured their safety with three points.
Leganes: Cuellar, Zaldua, Bustinza, Siovas, Rico, Perez, Appelt (Gumbau, 90+3), El Zhar, Eraso, Omar, Amrabat (Beauvue, 89)
Sevilla: Rico, Layun, Kjaer, Lenglet, Escudero (Arana, 78), N’Zonzi, Banega, Sarabia, Vazquez (Muriel, 72), Nolito (Sandro 63), Ben Yedder.