Real Madrid lost 2-1 at Sevilla on Wednesday in the aftermath of its stinging "clasico" defeat as it slipped behind in the Spanish title race, while Atletico Madrid and Barcelona kept winning to move ahead of their rival in the standings.
Cristiano Ronaldo put Madrid in charge with his league-leading 27th goal of the season in the 14th minute, but Sevilla striker Carlos Bacca scored twice, in the 19th and 73rd, to complete the comeback.
Madrid's loss at the Sanchez Pizjuan Stadium came four days after it squandered a chance to effectively end Barcelona's title defence, with Lionel Messi out-dueling Ronaldo by scoring a hat trick for a thrilling 4-3 win in the Spanish capital. These consecutive losses came after Carlo Ancelotti's side had gone undefeated for 31 straight matches.
"We have to keep working, fighting and ask our fans for forgiveness," said Madrid full back Marcelo. "It's tough to do what we did, to keep winning for so many games. We have lost two games. They aren't more important, but they are critical. Now everything is much more difficult."
Diego Costa's second-half header gave Atletico a 1-0 victory at home over Granada as it moved three points clear of Madrid with eight rounds remaining.
Lionel Messi and Neymar helped Barcelona stay one point behind Atletico as it rose into second place, but the 3-0 win over Celta Vigo came at the cost of goalkeeper Victor Valdes tearing a right knee ligament.
"I am happy for the goals and for having won the other day at the Santiago Bernabeu," said Neymar. "(But) the victory is sad because of Valdes' injury."
Ronaldo struck first at Sanchez Pizjuan Stadium when his free kick took a deflection off the arm of Bacca, catching goalkeeper Antonio "Beto" Bastos out of position and helpless as he watched the ball float into his net.
But Bacca equalized from Jose Antonio Reyes' pass after Xabi Alonso had lost possession. Madrid then wasted several chances, and Sevilla tilted the match in its favour in the second half when Ivan Rakitic used a superb control of a pass before playing Bacca clear to beat goalie Diego Lopez for the winner.
Sevilla extended its winning streak to six games in a row as it remained in fifth place.
Atletico stayed unbeaten at home in league play this season after limiting Granada's attack with its stout defence before Diego Costa turned home Jose Sosa's corner kick in the 63rd for his 24th league goal of the season.
Earlier at Camp Nou, Valdes' right knee buckled after a routine save in the 22nd, and he had to be shuttled off the pitch with his gloved hands covering his face. The club later said he will need surgery, which would rule him out for the season.
Neymar netted twice from passes by Alexis Sanchez. The Brazil striker opened the scoring in the sixth minute and struck again in the 67th after Messi recorded his 22nd league goal of the season on the half-hour mark.
Celta, coached by former Barcelona player and B-team manager Luis Enrique, never mounted a challenge and its high defensive line proved easy pickings for the Catalan side's passing game.
Messi got things rolling when he dribbled at Celta's defence and spotted Alexis's run down the right edge of the area, where he received Messi's pass and squared for Neymar to tap home.
After Jose Pinto went on to replace the injured Valdes, Messi took Andres Iniesta's pass, rounded 'keeper Yoel Rodriguez and fired the ball inside the upright for his eighth goal in his last four matches. Pain in his left leg kept Iniesta from returning after halftime, but he said he expected to be fit to play at Espanyol on Saturday.
The 38-year-old Pinto was tested in the 52nd and was up to the challenge when he made back-to-back reflex saves to turn away Augusto Fernandez's powerful strike and Santi Mina's follow-up attempt. He went on to make two more noteworthy saves.
Neymar hit a second time from a long pass by Alexis when he managed to slot the ball through two defenders and beyond Rodriguez.
Also, Rayo Vallecano beat Osasuna 1-0 thanks to Joaquin Lavirrey's 90th-minute penalty for its fourth win in five rounds to edge away from the relegation zone.