The Basque side, who have the smallest ground in the Spanish second tier and a miniscule budget compared to many of their rivals, defeated Alaves 1-0 to move top of the table.
And they were able to celebrate a guaranteed top-two finish within an hour of their match finishing as Las Palmas threw away a two-goal lead against Recreativo Huelva and lost 3-2.
However, Eibar could yet see their dreams dashed, as they must raise extra "share capital" of €1.7 million by August in order to comply with recently introduced financial regulations.
Should the club fail to generate sufficient funds, Eibar face dropping down a division to Segunda B rather than having the chance to rub shoulders with the likes of Real Madrid and Barcelona.
Real midfielder Xabi Alonso, who enjoyed a loan spell at Eibar more than a decade ago, is among those to have spoken out in support of debt-free Eibar, insisting they deserve to be rewarded for their on-pitch achievements.
Meanwhile, Deportivo La Coruna, who led the table heading into Sunday's fixtures, must wait to confirm a return to La Liga after they slumped to a 2-1 defeat at Numancia.
With two games still to play, Deportivo are six points clear of the play-off places but have now failed to win in five matches.
