Eibar crushed Sevilla 5-1 in the Spanish league on Saturday, while Real Betis forward Loren Moron scored twice in his debut.
Eibar outclassed an inexperienced Sevilla side that included Sandro Ramirez, Miguel Layun and Roque Mesa making their debuts following their arrivals in the final days of the January transfer market.
Fabian Orellana led Eibar with two goals. Enrique Garcia, Ivan Ramis and Anaitz Arbilla also netted for the Basque Country hosts.
Pablo Sarabia got Sevilla's only goal from the penalty spot in the first half to make it 2-1.
Sevilla coach Vicenzo Montella has managed to win once only in five rounds since replacing Eduardo Berizzo.
Sevilla faces an important match on Wednesday when it hosts Leganes in the return leg of the Copa del Rey semifinals after a 1-1 draw in the first match.
"I want to ask our fans to forgive us (for the loss), but I am sure that if we stay united we can reach the final (of the cup)," Montella said.
Eibar, whose budget of around 50 million euros is a third of Sevilla's, climbed to seventh place and to just one point behind Sevilla in sixth after losing only once in its last 11 league matches.
Eibar coach Jose Mendilibar said his team's performance was among its very best since the club joined the first division 3 1/2 seasons ago.
"Given the rival, the way we played, the occasions we created, what we didn't let them do . today we played a complete match in every sense," Mendilibar said.
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DREAM DEBUT
Loren Moron enjoyed a dream debut for Betis' first team in a 2-1 win when the reserve team forward struck twice to help down a Villarreal side that played with 10 men for an hour.
Daniele Bonera saw a direct red card in the 31st for a dangerous tackle of Ruben Castro.
Moron struck from outside the area in first-half stoppage time and added a second goal in the 65th.
Carlos Bacca pulled one back for Villarreal by scoring a penalty after Denis Cheryshev was fouled by Antonio Barragan.
Villarreal was left in fifth place, while Betis moved into ninth.
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