Atletico Madrid defeated Real Betis to pick up crucial three points and move up to 4th position in the league table. Nicolas Gaitan scored the only goal for Diego Simeone's side.
In another important match, FC Barcelona came back to winning ways in the La Liga with a thumping 5-0 win over minnows Las Palmas.
It was a much-needed win after a disappointing 1-1 draw against Villarreal last week. Luis Suarez and Lionel Messi, as usual, architected the win for Barcelona.
The Uruguayan star scored a brace and Lionel Messi, Aleix Vidal and Arda Turan netted one each to guide the Catalan giants to a brilliant win.
Real Madrid's unbeaten streak finally comes to an end after 40 matches as they conceded a 2-1 defeat against Jorge Sampaoli's Sevilla.
Cristiano Ronaldo scored the opening goal for Real Madrid in the 69th minute from a penalty but an unfortunate own goal from captain Sergio Ramos restored parity. Stevan Jovetic scored the winning goal for the home side.
Here are all the results from game week 18, Day 1
Leganes 0-0 Athletic Bilbao
Barcelona 5-0 Las Palmas
Atletico Madrid 1-0 Real Betis
Deportivo 0-0 Villarreal
January 15, Sunday
Valencia 2-1 Espanyol
Celta Vigo 1-0 Alaves
Granada 1-1 Osasuna
Sporting 2-3 Eibar
January 16, Monday
Sevilla 2-1 Real Madrid
January 17, Tuesday
Malaga 0-2 Real Sociedad