Barcelona made it four La Liga games without a win on Saturday after failing to beat 10-man Alaves, a 1-1 draw leaving Ronald Koeman's side sitting 12th in the table.
Luis Rioja put Alaves in front at Mendizorrotza after an error from Barca's back-up goalkeeper Neto, with Antoine Griezmann equalising in the second half, a minute after Jota Peleteiro had been sent off.
But with almost half an hour left and an extra man, Barcelona were still unable to find a winner, instead settling for a draw to go with recent defeats by Getafe and Real Madrid, and another draw against Sevilla.
It means Madrid, who had earlier won 4-1 at home to Huesca, now sit eight points clear of their Catalan rivals, having played a game more, while Atletico are six ahead after they beat Osasuna 3-1. Atletico will go top if they win their game in hand.
Even at this early stage in the title race, the gap is significant and Koeman will know the scrutiny on his position as coach will increase, particularly after the resignation of Josep Maria Bartomeu as president on Tuesday.
Bartomeu appointed Koeman coach in August and eight points from the first six league games is not the sort of form that will impress the next president and board, who should be voted in before the end of January.
"I'm very disappointed," said Koeman. "Once again we haven't played well enough to get a result. The first goal was a gift and then we created a lot of chances but didn't take them."
Koeman's decision to substitute Ansu Fati with 12 minutes left was particularly surprising given Fati had been arguably Barcelona's most dangerous player, perhaps even more threatening than Lionel Messi, who endured a frustrating night.
Messi has still not scored in open play this season and while he was at the heart of almost every Barca attack, his touch and finishing was again not as crisp as usual. He was booked in the first half for dissent.
Fati and Griezmann both missed early chances while a Messi free-kick would have gone in had Florian Lejeune not been perfectly placed on the line.
Frenkie de Jong was unlucky not to have had a penalty when nudged out of a free header by Ximo Navarro before a Barca mistake gifted Alaves the opening goal.
Gerard Pique underestimated how close Neto was to him and the defender's firmly hit backpass caught the goalkeeper by surprise. Neto failed to adjust his feet and Rioja capitalised, robbing him of the ball and tapping into an open net.
Koeman made three changes at half-time, with Pedri, Francisco Trincao and Miralem Pjanic all coming on.
But Barca found it difficult to break down the Alaves defence until Peleteiro gave them an opening. He booted Pique in the face to earn a second yellow card in the 62nd minute and in the 63rd, Griezmann equalised, an exquisite, lifted finish pulling Barcelona level.
It was almost 2-1 a minute later but Messi's finish was well saved while Griezmann had a second ruled out for offside. Fati fired at goal before going off and Pique's finish was cleared off the line. Alaves held on.
- Hazard ends goal drought -
Eden Hazard earlier scored his first goal for Real Madrid in over a year and his team appear to have turned a corner after their comfortable win over Huesca.
Hazard has had a terrible time with injuries since joining Madrid for 100 million euros from Chelsea in 2019 but the Belgian will hope his stunning strike from distance at the Alfredo di Stefano can kick-start his career in Spain.
"We know the quality that Eden has," Zidane said. "He scored a good goal and we needed it in the first half, because after his first goal the game was different."
Karim Benzema and Fede Valverde made the win secure before Huesca scored through David Ferreiro, only for Benzema to add his second and Madrid's fourth in injury-time.
It caps an encouraging week for Zidane's side, which began with the Clasico win at Camp Nou and finishes with them top of the table, two points ahead of Real Sociedad.