Defending champions Real Madrid have suffered a shock 1-0 Spanish La Liga home defeat to Villarreal.
To add salt to their wound, Atletico Madrid and Valencia both won later in the day.
Zinedine Zidane's Los Blancos went into their league clash on 32 points -- 16 adridt of pacesetters Barcelona -- and that's where they remained after a sublime finish from Pablo Fornals finished off an 87th-minute counter-attack from the Yellow Submarine.
Villarreal had had goalkeeper Sergio Asenjo to thank for a number of vital saves in the win that lifted them to fifth, just a point behind Real.
"There is no explanation for this," Zidane said.
"We did everything we could, we had plenty of chances, but the ball just didn't go in.
"It's a difficult moment for us. It's tough for the players, they gave their best.
"We didn't deserve this result."
After Gareth Bale had his header correctly ruled out for offside, Asenjo saved superbly from Marcelo's thunderous drive and Cristiano Ronaldo's free-kick, before also denying the Portuguese forward from close range on the stroke of halftime.
Asenjo made a number of more routine saves in the second period before the visitors cleared a late Real corner and set Denis Cheryshev clear down the left.
The halftime substitute found Enes Unal in the centre of the penalty area and, although Unal's shot was blocked by the onrushing Keylor Navas, it landed for Fornals to chip a first-time shot over the despairing goalkeeper.
Second-placed Atletico Madrid were indebted to their goalkeeper, Jan Oblak, as they closed the gap at the top to six points with a 1-0 victory at Eibar.
The visitors scored what would prove to be the only goal of the game in the 27th minute.
Antoine Griezmann cut the ball from the right towards Kevin Gameiro, who slotted past the onrushing Marko Dmitrovic from close range.
"We played the type of match we needed," Atletico coach Diego Simeone said.
Valencia won 2-1 at Deportivo La Coruna to move up to 40 points.
Los Che, who handed a debut to new signing Francis Coquelin from Arsenal, took the lead on 37 minutes after a blunder by Deportivo goalkeeper Ruben.
Goncalo Guedes tried his luck with an angled effort from 20 yards, which squirmed under the keeper at the near post and rolled into the net.
Rodrigo added a second on 64 minutes with a deflected shot from the edge of the penalty area.
Florin Andone headed in a late consolation for the home side with three minutes left.
Michael Olunga scored a 22-minute hat-trick as Girona thrashed bottom club Las Palmas 6-0 at Montilivi.
The Kenyan striker, who is on loan from Chinese club Guizhou Zhicheng, struck in the 57th, 70th and 79th minutes to become the first player to record a Spanish top-flight treble for Girona.