Rayo Vallecano waltzed to a 3-0 victory over Atletico Madrid on Sunday in LaLiga, leaving Diego Simeone's side 15 points behind leaders Real Madrid.
Atletico dropped to fourth after their heavy defeat at Leganes's Butarque stadium, where Rayo hosted the fixture due to pitch problems at their own Vallecas ground.
Fran Perez, Oscar Valentin and Nobel Mendy struck for Rayo, who thoroughly deserved their triumph against an Atletico side that had thrashed Spanish champions Barcelona 4-0 in the Copa del Rey on Thursday.
With the Spanish cup their best chance of silverware this season it has seemed that Atletico have lacked some focus in LaLiga, and that was reflected in this humbling by their city rivals.
The Rojiblancos have not won in their last three league matches.
"It seems like the league has slipped away, we can't lose games like this and we can't play a game the way we did today," angry Atletico goalkeeper Jan Oblak told DAZN.
"Competing like this is going to be to tough, you can't choose your games, every game has to be played at the highest level...
"Today they were much better, congratulations to them, we lost and deserved to lose."
'THEY WERE BETTER'
Simeone, who rotated much of the team that beat Barca with Wednesday's Champions League playoff against Club Brugge in mind, did not agree with all of Oblak's analysis.
"I don't share (his opinion), I thought the team gave what it could, they were better, but the truth is there is no need to criticise the team in terms of effort, work, of wanting to do well," said Simeone.
"We didn't have a good match, the opponent was better, congratulations to them and let's think about what's coming on Wednesday."
Inigo Perez's Rayo took the lead in the 40th minute when Perez finished Andrei Ratiu's cross, and Valentin doubled their advantage after Clement Lenglet gave the ball away.
Mendy netted the third in the 76th minute after some more poor Atletico defending to round off a miserable afternoon for Simeone's side.
Rayo, whose players have complained in recent weeks about the way the club is being run, as well as the state of the Vallecas pitch and their training ground facilities, backed by the coaching staff, climbed up to 16th.
"This is a battle-hardened team that adapts well to circumstances," said Rayo coach Perez.
"Today's match was very tough both because of the opponent and because of our own institutional and sporting situation."