Leganes will join Alaves in La Liga next season after they beat Mirandes 1-0 on Sunday to secure automatic promotion at the expense of Gimnastic.
Pablo Insua’s header from a corner just before half-time was enough to send Lega into the Spanish top flight for the first time in their history.
The match did not end without controversy, however, as Aridane Santana’s late goal for Mirandes was adjudged offside, despite replays showing the decision to be incorrect.
Nonetheless, Alaves’ last-gasp equaliser against Nastic put the decision in vain as the goal would not have made a difference in the promotion race had it counted.
Leganes will join Real Madrid and Atletico as the third Madrid-based club in La Liga next season following Getafe and Rayo Vallecano’s relegation.
Elsewhere on a fateful final day in La Segunda, Nastic were joined by Girona, Cordoba and Osasuna in the playoffs, while Mallorca’s 1-0 win against Tenerife sent down Ponferradina.
Image courtesy @CDLeganes via Twitter
See the latest La Liga predictions and betting tips with Eurotips.co.uk