Alaves saw their winning streak at the Estadio Ipurua, falling to defeat in injury time.
The visitors scored early thanks to a goal by Manu Garcia, but Eibar were on terms with 20 minutes to go before Diop's late, late winner.
It was a game marked by controversy and VAR, however.
There were two red cards, a penalty decision that was missed and an Alaves goal ruled out.
It was the sending off of De Blasi which helped Los Armeros come back into the match.
First Jordan had everyone off of their seats, and with the very last kick, Diop stunned the visitors, who would've moved to within a point of leaders Barcelona had they held on.