Real Zaragoza blew the Spanish title race wide open with a 1-0 home win over reigning champions Barcelona on Saturday, the only goal of the game coming from Argentine sharpshooter Diego Milito.
Barcelona still lead La Liga by two points but would lose pole position with nine games remaining if Sevilla beat Racing Santander yesterday.
"It wasn't our night but they deserved this result. They scored and we didn't have the capacity to change the result," Barcelona coach Frank Rijkaard admitted.
Milito found the net after 58 minutes, chipping the ball past Barca goalkeeper Victor Valdes from close range after an oustanding pass from close to the touchline by his Argentine compatriot Andres D'Alessandro.
"This was revenge for Barca beating us here and knocking us out of the [Spanish] Cup in February. I think we were up for this game from the very first minute," Milito added.
Milito's 19th goal of the season makes him the joint top scorer in the Spanish first division, and was a just reward for Zaragoza being the best side up to that point.
First half chances fell to D'Alessandro, Carlos Diogo and Sergio Garcia but Barca grimly held on until the break.
Barca almost equalized within seconds of Milito's goal but Zaragoza goalkeeper Cesar Perez came out on top a one-on-one situation with Deco and the visitors never had a better chance in the remaining half hour.
Zaragoza are now unbeaten in seven games and are in contention to qualify for the Champions League for the first time.
"Overall this was our best 90 minutes of the season. They way that Barca play means that this was always going to be an open game and so we had the chance to surprise them. We beat them by playing football," Zaragoza coach Victor Fernandez reflected.
Barcelona were without their three-time African Player of the Year Samuel Eto'o, who sustained a muscle strain at the top of his right leg in training earlier this week.
Media speculation in Spain suggested Eto'o had actually been left out to prevent more racist taunting of the Cameroon striker, but it was a suggestion strongly refuted by Barcelona coach Frank Rijkaard.
"His absence is because he's not fit to play. For us, it's always better if he's with the team," Rijkaard said on Friday.
Eto'o threatened to walk off the pitch during last season's match at Zaragoza after receiving racist abuse from the home crowd.
Zaragoza moved up to fourth place, ahead of Valencia on goal difference, after the 2002 and 2004 Spanish champions went down 1-0 at struggling Athletic Bilbao later on Saturday.
Athletic's Igor Gabilondo got the only goal of the game with a cheeky right foot back-heel after 27 minutes, following a pass from Joseba Etxeberria.
Valencia piled on the pressure in the second half in a bid to get an equalizer but just came up short.
David Villa hit the cross bar after 78 minutes and then, six minutes from time, Valencia's Spanish international striker sent a free kick from 30m just centimeters past the post.
The victory means Athletic climb out of the relegation zone and improves their chances of keeping their historic status of being ever-present in the Spanish first division although every other team in the bottom half of the table played yesterday.