Barcelona's title defence was derailed as Villarreal romped to a sensational 5-3 victory in LaLiga Saturday with three late goals.
After Real Madrid moved two points clear of Girona at the top of the league with a 2-1 win at Las Palmas, the pressure was firmly on Xavi Hernandez's defending champions in third.
In a see-saw match Gerard Moreno and Ilias Akhomach put Villarreal two goals ahead before Barca battled back.
Ilkay Gundogan and Pedri Gonzalez struck before Eric Bailly headed into his own net to give the hosts the lead.
However Goncalo Guedes fired home in the 84th minute before stoppage time strikes from Alexander Sorloth and Jose Luis Morales left Barca 10 points adrift of rivals Real.
"It was not a good game, but if you're two goals down and then 3-2 up, you cannot give that away," Barca midfielder Frenkie de Jong told DAZN.
"We have to improve because this...I think that it cannot happen at a top team."
Xavi brought in Joao Felix and midfielder Oriol Romeu from the side that lost in extra-time against Athletic Bilbao in the Copa del Rey in midweek, as well as young defender Hector Fort.
After that elimination and a thrashing by Real in the Spanish Super Cup final, Barca have only LaLiga and the Champions League left on the table.
Barca's 16-year-old sensation Lamine Yamal offered spark and invention on the right but Villarreal were the more dangerous side in the first half.
Barca have conceded far too many early goals this season and after three minutes Alex Baena struck, but it was ruled out for offside.
Felix had a vicious strike tipped over by Filip Jorgensen before Villarreal had another strike disallowed, controversially.
Moreno rifled in at the near post but Alexander Sorloth was ruled to be offside and blocking defender Ronald Araujo.
It was third time lucky for the Yellow Submarine, however, with Moreno firing home Sorloth's cut-back with aplomb - this time it counted.
As the players trudged in for half-time Barca were whistled by disgruntled supporters at their temporary home at Olympic Stadium.
Xavi made a triple change at the break, throwing on Joao Cancelo, Pedri and 17-year old defender Pau Cubarsi.
It fired the team up as they pushed Villarreal back, but they conceded a foolish second goal after a bad Cancelo mistake.
The defender miskicked the ball allowing former Barca winger Akhomach to gallop in on goal, rounding Inaki Pena and rolling home.
Undeterred, Barca fought their way back in.
Gundogan finished superbly after Robert Lewandowski diverted the ball into his path on the edge of the box after an hour.
Then Pedri drove home eight minutes later to level the scores, before Bailly headed Gundogan's free kick into his own net.
Barca substitute Vitor Roque came close to adding a fourth but Jorgensen saved his low strike after he raced in behind.
However Barca's defence, a far cry from the watertight back-line which led them to the title last season, was pulled apart again by Sorloth.
The striker fed winger Guedes, who flashed a strike past Pena and into the far corner.
Barca were awarded a penalty in the 90th minute when Santi Comesana blocked Gundogan's cross with his elbow but the referee cancelled it after reviewing the incident on Video Assistant Referee, leaving the hosts furious.
Worse was to come, with Sorloth finishing from close range to put Villarreal ahead and Morales rubbed salt in the wound with a late fifth, with Barca in total disarray.
It was Villarreal's first win in five games in all competitions and their coach Marcelino's first ever against Barca in 21 matches.
"It was time for us to have some joy like this," said striker Moreno.
"It's turning out to be a tough season and the fans deserved something like this."
RESULTS
Sociedad 0 Vallecano 0
Las Palmas 1 (Munoz 53) Real Madrid 2 (Vinicius 65, Tchouameni 84)
Barcelona 3 (Gundogan 60, Pedri 68, Bailly 71-og) Villarreal 5 (Moreno 41, Akhomach 54, Guedes 84, Sorloth 90+9, Morales 90+12)
Mallorca 0 Betis 1 (Altimira 45+1)
Friday
Almeria 0 Alaves 3 (Omorodion 10, 88, Rioja 52-P)
