Real Madrid took full advantage of Barcelona's first loss of the season in the La Liga, by obliterating Valencia 5-0 Sunday.
Barcelona tasted defeat for the first time in 20 La Liga games, going down 3-2 to Real Sociedad, after leading 2-0 at one time, with the game turning on its head following the sending off of Gerard Pique.
The results leave Barcelona with still a sizeable eight-point lead over second-placed Atletico Madrid, who won 2-0 against Levante, thanks to goals from Adrian Lopez and Koke, with the gap between Real and Barca reduced to 15 points.
A brace each from Cristiano Ronaldo and Angel Di Maria, coupled with the opening strike from Gonzalo Higuain gave Real the easiest of wins against a surprisingly poor Valencia side.
Higuain got things rolling in the ninth minute, firing home off a cutback from Di Maria. The Argentine winger then made it 2-0, tapping home from close range after some brilliant work from Ronaldo in the 34th minute.
The Portuguese superstar, not one to miss out, got on the scoresheet two minutes later, before the Ballon d'Or runner-up smashed home the fourth in the 41st minute.
Di Maria added the gloss in the final minute of the first half, with Real cruising in the second period to take home a deserved three points.
"It was a match that we made easy for ourselves," Di Maria said. "We did things well from the start. It was important to keep our winning streak going.
"There are some matches that are difficult and others that are easier, but this time we had a great match and we went out to press forward as we have been doing and we got a lot of goals.
"It is an important win and means that we keep closing the gap."
At Sociedad, Lionel Messi opened the scoring for Barca in the seventh minute, drilling home a shot from just outside the box. In the 25th minute, the league leaders were seemingly in cruise control as Pedro got in on the end of a cross from Dani Alves to double their lead.
Chori Castro gave Sociedad hope by reducing the deficit in the 41st minute, before Pique's sending off for a second yellow card in the 56th minute changed the game completely.
Castro again made his mark, seeing his shot take a wicked deflection off Javier Mascherano and creep into the net.
Sociedad then struck the killer blow, with the match seemingly on its way to a draw, in the final moments with Imanol Agirretxe proving to be the hero, turning in a cross into the back of the net.
"We have to congratulate them," Barcelona manager Tito Vilanova said. "Their victory was achieved more because of their effort than because of our mistakes.
"I cannot reproach my players. In the first half we controlled the game and we hit the woodwork twice and another chance was saved by Bravo. We played against a team that had only allowed six goals at home."
Results: Valencia 0-5 Real Madrid; Getafe 1-1 Sevilla; Valladolid 2-0 Zaragoza; Atletico Madrid 2-0 Levante; Osasuna 2-1 Deportivo; Malaga 1-1 Celta; Real Sociedad 3-2 Barcelona; Murcia 2-0 Rayo Vallecano; Espanyol 3-2 Mallorca.