Reigning Spanish and European champions Real Madrid have started the season below their brilliant best and this week finally tumbled to a first defeat since January.
Carlo Ancelotti's side were beaten at Lille in the Champions League on Wednesday and trail Hansi Flick's Barcelona by three points in La Liga.
Madrid host Villarreal on Saturday aiming to pull level on points with their Catalan rivals at the top of the table for the first time this season.
Los Blancos began the campaign with a draw at Mallorca on the first day of the season and have been playing catch-up since then.
Barca won their first seven matches in a row but finally stumbled last weekend at Osasuna.
Madrid could not take full advantage as they were held to a 1-1 draw by neighbours Atletico Madrid, but can put pressure on Barca, who visit Alaves on Sunday, with a victory at the Santiago Bernabeu.
To achieve that against an enterprising Villarreal side just a point behind Madrid in third, they will have to raise their game significantly.
Madrid came undone in the north of France, suffering their first loss in 37 matches across all competitions.
"When we lost the derby (against Atletico) last year it was a fantastic wake-up call and hopefully this defeat can also be a fantastic wake-up call," said Ancelotti.
"We did everything wrong -- with the ball, transitions, the intensity, we lost the duels... we have to look at things with a cool head and not throw everything away, but we have to improve."
Madrid were able to bring on Kylian Mbappe against Lille after a thigh injury and the French striker could start against Villarreal.
As strong as the Yellow Submarine have been, spearheaded by Spain international Ayoze Perez, they have conceded in every match so far this season.
Madrid still seem to be struggling without midfield maestro Toni Kroos, who retired after helping the team to a La Liga and Champions League double.
Los Blancos will also line up with Ukrainian goalkeeper Andre Lunin between the sticks with Thibaut Courtois out injured.
"We have to analyse and improve in the next game because there is no time -- there are many games and we have to win," said Lunin after the Lille defeat.
Villarreal may be without Perez, who missed Monday's win over Las Palmas with muscular discomfort and Gerard Moreno is also sidelined, but striker Thierno Barry is finding form for Marcelino Garcia Toral's side.
The French striker scored and got an assist as Villarreal moved up to third with the 3-1 win.
Girona and Atletico Madrid also suffered Champions League defeats on Wednesday and both are in action on Sunday, against tricky Basque sides Athletic Bilbao and Real Sociedad respectively.
Player to watch: Jesus Navas
The Spanish veteran wide man will play in the Seville derby for what is due to be the final time of his career, and become the player with the most appearances in the clash's history -- he has played in it 27 times, level with Real Betis legend Joaquin Sanchez. Sevilla's Navas, who turns 39 in November, is playing through a long-term hip problem, and is due to retire in December.
