Lionel Messi was short of fitness and Barcelona lacked spark as a goalless draw away to Athletic Bilbao on Sunday offered fresh hope to their rivals in the title race.
A thigh injury had limited Messi to 27 minutes against Real Madrid on Wednesday and while he played the full match at San Mames, Barca's assistant coach Jon Aspiazu had admitted before kick-off he was not yet 100 per cent.
In all likelihood, he stayed on because his team needed him but Messi was not at his best and neither were Barcelona, who would even have lost had it not been for Marc Andre ter Stegen's stunning late save to deny Inaki Williams.
"He saved us," coach Ernesto Valverde said. "It was a great stop."
The draw makes it three games without a win for La Liga's leaders, whose advantage is still six points but now with Real Madrid their closest challengers, after they beat Atletico on Saturday.
"We were first last week and we are still first, and if my maths is right, we will be again next week," Valverde said.
But Real's victory at the Wanda Metropolitano was their fifth on the bounce and just as they have gained momentum, Barca appear to be losing theirs, at a crucial juncture, with more stern tests to come.
After Real Valladolid at home next weekend, Valverde's side travel to Lyon in the Champions League and Sevilla in the league. They then face two Clasicos in four days, one in the Copa del Rey, and both at the Santiago Bernabeu.
"We are playing a lot of games at the moment and that shows," Luis Suarez said. "We also lacked communication today -- it is the little details that make a difference."
Injuries have not helped either. Messi was picked but not fully recovered while Ousmane Dembele was fit enough only for the bench, having shaken off an ankle injury.