Real Madrid lost 1-0 away to Osasuna on Sunday to allow Barca, which won 3-0 away to Hercules on Saturday, to take a seven-point lead at the top of the Spanish top flight soccer.
Javier Camunas scored a second half goal to give relegation threatened Osasuna three vital points and at the same time knock the wheels off Real Madrid's title challenge.
Jose Mourinho's side are now seven points behind a Barca side that has only dropped five points all season and without Xabi Alonso, who missed most of the match with a fever, Real Madrid looked flat and lacking ideas.
Villarreal remain third after a 1-0 win over an Espanyol side thanks to Giuseppe Rossi's 12th goal of the season. The Italian had signed a new contract in midweek and celebrated in the best possible style.
Athletic Club Bilbao took a huge step towards qualifying for Europe with a 2-0 win away to Atletico Madrid.
Gaizka Toquero scored his first two goals of the season to give the Basque side a well-deserved win, although Atletico were unlucky to have Luis Perea sent off for committing a penalty on Fernando Llorente, which the striker then missed.
The bulk of the games were played on Saturday and FC Barcelona continued their incredible form with a 3-0 win away to Hercules.
Leo Messi scored twice after Pedro Rodriguez opened the scoring for Barca as the Catalans won their fifteenth consecutive game, to equal the record set by Real Madrid in the 1960-61 season.
The win saw Barcelona avenge the only league defeat they have suffered this season when Pep Guardiola's side lost 2-0 to the side from Alicante in the Camp Nou Stadium.
Real Sociedad beat struggling Almeria thanks to goals from Ion Ansotegi and Raul Tamudo to move into a comfortable mid-table position.
Sporting Gijon produced the shock of the day as they continued their revival with a 4-0 win away to Mallorca.
Sporting have now taken 10 points from four matches to climb away from the relegation zone. Diego Castro, Kevin, Andre Castro and Nacho Novo all scored to give the visitors their first away triumph of the season.
Zaragoza also continue to improve under Javier Aguirre and goals from Nicola Bertolo and Sinama Pongolle gave them all three points in Malaga after the home side had taken the lead thanks to Sergio Barbosa's opening strike for the home side.
Getafe's dreadful recent form continued with a 2-0 defeat away to relegation threatened Levante. Valmiro Lopez and Felipe Caicedo scored early in the second half, while Getafe also had Manu del Moral sent off for aggression.
Deportivo la Coruna and Sevilla produced a thrilling match in the Riazor Stadium which ended in a 3-3 draw. Sevilla keeper Andres Palop was sent off early in the game and Lassad Nouioui scored twice to put Deportivo 2-0 ahead.
Sevilla showed character and Alvaro Negredo twice and Julian Escude scored to turn the tables and give Sevilla a 3-2 lead.
Laureano Ruiz equalized for Deportivo four minutes from time and the home side almost won the game in injury time as Sevilla's reserve keeper Javi Vargas did well to save a powerful shot from Juan Rodriguez.