Jose Mourinho suffered his first home defeat as a coach since February 23, 2002 with FC Porto, when Real Madrid fell 1-0 to Sporting Gijon thanks to Miguel de las Cuevas' strike.
Cuevas, a former Atletico Madrid player, netted the only goal of the game in the 79th minute after he broke free on the edge of the area and fired in a right footed shot off the post.
The defeat means Madrid find themselves eight points adrift of Barcelona after the league leaders beat Villarreal, and is a blow to morale ahead of Tuesday's Champions League quarter-final first leg against Tottenham.
Even the return of Gonzalo Higuain after more than four months out through injury could not help Madrid, who badly missed key players such as Cristiano Ronaldo, Karim Benzema and Xabi Alonso.
Mourinho, who conceded that eight points was ''practically impossible'' to overcome, said after the game: ''Our opponents defended, defended and defended. They had one chance and they scored one goal. I praised them because they fought a lot and they fought to try to have luck on their side. We had four, five, six chances to score and we couldn't. That's football and tomorrow's another day.
''We played without the team's most creative players. We lacked creativity. We had to try a different style, more direct with long balls in the air, and we had more opportunities.
''If I had wanted to draw the game 0-0 from the start I would have done so. But a draw was a bad result. Against Tottenham on Tuesday, it won't be. If we draw at home, it would not be a drama because we will have the return to play in London.''
Madrid defender Sergio Ramos added in AS: ''A large part of the league has gone away from us. There are very few points left. We can't reproach the team for anything. Unfortunately the ball did not go in today. It's very sad to lose with so many chances.''
Barcelona were made to work for their win, but they picked up a vital three points with a 1-0 victory at high-flying Villarreal.
Goalkeeper Victor Valdes was tested early on, making some crucial saves, and the Spanish champions were forced to bring Lionel Messi on from the bench after the break. They eventually made the breakthrough from a set-piece as Sergio Busquets' flick-on fell to Gerard Pique in the box and the Spanish defender calmly chested the ball down before hammering it into the net for his second goal of the season.
Villarreal almost snatched a point in the 85th minute, but Santi Cazorla's volley was somehow turned over the bar by Valdes from six yards out.
In the day's other game, Roberto Soldado scored all four goals as Valencia came from 1-0 down to claim an emphatic 4-2 victory at Getafe as they further continued their hunt for an automatic Champions League spot.
Manu gave Getafe a 13th-minute lead and there was little sign of what was to come before Soldado levelled just after half-time. It heralded a spell of four goals in 31 minutes and although Adrian Sardinero grabbed a late consolation, it was Soldado's night.