Barcelona clung on with 10 men to beat Valencia 1-0 and move nine points clear of Real Madrid at the top of La Liga on Sunday, thanks to Raphinha's early header.
The champions could not find a way through against Real Betis in an entertaining 0-0 draw later on at the Benito Villamarin.
Brazilian winger Raphinha nodded Barca in front in the 16th minute. But after Ferran Torres missed a penalty and Ronald Araujo was sent off, the hosts were left fighting tooth and nail for the three points.
They retreated in the final half hour following Araujo's 59th minute red card but survived to beat Ruben Baraja's Valencia, who are 19th and two points from safety.
"We suffered too much, we had many chances to score the second," Xavi told reporters.
"It can't be that we have to finish games like that when we have chances. We have to learn how to close out games."
Barcelona's 1-0 Copa del Rey semi-final first-leg triumph over Madrid on Thursday followed two consecutive defeats, and this narrow victory felt like a significant step towards a first league title since 2019.
Without top scorer Robert Lewandowski, midfield maestros Pedri and Gavi and winger Ousmane Dembele, the Catalans did just enough to win.
Valencia resisted early Barcelona pressure but came undone when Sergio Busquets lofted a pass into the area for Raphinha to meet with a cunning run and a header over Giorgi Mamardashvili.
Samuel Lino missed a big chance for Valencia in the first half, and early in the second Barcelona should have moved two ahead when Hugo Guillamon was penalised for handball.
Torres grabbed the ball to take the penalty, although Ansu Fati also wanted it and the pair exchanged words, increasing the pressure on the Spaniard, who hit the post.
Fati hit the woodwork himself moments later, before a mistake from Jules Kounde left Barcelona with 10 men.
The French defender's header back towards his own goal sent Hugo Duro through. Araujo dragged down the striker and saw red.
Valencia put pressure on Barcelona without troubling Marc-Andre ter Stegen, who kept his 18th La Liga clean sheet of the season.
The visitors might have been awarded a late penalty when Franck Kessie tangled with Fran Perez, but the referee waved away their desperate – and not unfounded – appeals.
"I thought the referee was going to blow for (the penalty), he steps on him and there's contact," said Valencia's Hugo Guillamon.
Reigning champions Madrid forged the better openings against Betis but could not find the goal they needed to stay as close as possible on Barcelona's tail.
Karim Benzema had a free-kick strike disallowed while Betis goalkeeper Claudio Bravo made fine saves to deny the French forward and Vinicius Junior.
Thibaut Courtois was also forced into two superb stops by Betis who showed why they are in contention for a Champions League place next season with a hearty performance.
"It's quite evident what we're lacking, we have to be more efficient," Madrid coach Carlo Ancelotti told Movistar.
"Sometimes opponents close up at the back, but we have the quality and we have to do it better."
The coach did not think his team's title defence was over, despite the setback.
"It's not impossible. It's very difficult, but we have no doubt we will try until the end," added Ancelotti.
Madrid winger Vinicius, as has become customary in La Liga, was engaged in a running battle with the Betis defence.
Vinicius has not scored away from home in the top flight since August, but brilliantly set up Benzema at the start of the second half with former Barcelona stopper Bravo parrying the effort.
It was Madrid's first shot on target since last weekend's 1-1 draw against Atletico Madrid.
Los Blancos have scored just once in their last three games – from a corner.
"I'm more upset than angry," said Ancelotti.
"I'm upset that this team, with this quality, can't score a goal in three games (from open play)."
Courtois made a stunning save to thwart Borja Iglesias at the other end, when the striker seemed poised to score.
"We had moments in which we had clear openings, my chance with Thibaut," Iglesias told Movistar.
"That's why this guy wins what he wins – he saves a lot."
Real Valladolid climbed to 14th with a 2-1 over Espanyol, while Rayo Vallecano and Athletic Bilbao shared a 0-0 draw.
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