Barcelona is fifth points ahead of Real Madrid at the top of La Liga thanks to its 3-0 win at Valladolid on goals by Xavi, Dani Alves and Lionel Messi.
Real beat Malaga, 2-0 on Sunday thanks to two goals by Cristiano Ronaldo, who was later sent off.
Barca has 49 points after 19 games thanks to 15 wins and four ties.
ATHLETIC BILBAO. In 1929-30, Athletic finished the first half of La Liga's second season unbeaten and went on to win the title without losing a game. Two years later, Athletic was also undefeated at the halfway mark, but it lost the league title to Real Madrid.
ESPANYOL. A year later, the same thing happened to Espanyol, which led at the break without a defeat but lost the championship to Real Madrid.
REAL MADRID. Real was unbeaten at the halfway point in 1966-67 and again two years later when La Liga expanded from 16 to 18 clubs. It finished the first half unbeaten again in 1979-80 and in 1988-89 when La Liga consisted of 20 teams and again in 1996-97 when it had 22 teams.
REAL SOCIEDAD. The last team to go unbeaten at the halfway mark was Real Sociedad in 2002-03. Unfortunately, it lost six games in the second half of the season and finished second, two points behind Real Madrid.