Xavi declared Barcelona's slender 1-0 win over Athletic Bilbao as a "golden victory" after they survived a late onslaught to restore their nine-point lead ahead of next weekend's Clasico.
Raphinha's first-half goal at San Mames ultimately proved decisive, but that was just the tip of the iceberg as Barca were forced to withstand intense late pressure.
Earlier, Raul Garcia had hit the post for the hosts, and Athletic's late barrage began with Alex Berenguer striking the woodwork.
Athletic thought they salvaged a dramatic draw when Inaki Williams surged clear and smashed home, but the goal was then disallowed after a VAR check, with Iker Muniain deemed to have handled in the build-up.
Nico Williams then somehow failed to properly connect with the ball when seemingly destined to convert a tap-in; the follow-up by Yuri Berchiche was cleared off the line; and Gorka Guruzeta's volley from that rebound was crucially blocked in front of goal by Andreas Christensen.
It was a valuable win with Barca set to face second-placed Real Madrid at Camp Nou on Sunday.
"The same thing has happened to us again," Xavi told reporters. "We have been at a good level for 75 minutes, although we have to attack better.
"It was a difficult game. In San Mames you end up suffering, and that's what happened. It's a golden victory for us and we take three very important points.
"We maintained the nine-point lead, and we go into the Clasico with confidence.
"But we have to get better offensively. We had two or three clear chances in the second half: from Ansu [Fati]; from [Alejandro] Balde, who didn't choose well; from [Robert] Lewandowski with a header.
"We have to improve in that aspect, be calmer and more patient and play more in the attacking half. Defensive solidity must also be valued, but it's true that we have to improve in the attack."
Barca were greeted with a particularly vociferous reception at San Mames in light of the Negreira scandal.
Last month, broadcaster SER Catalunya alleged Barca had paid €1.6million to the company of Jose Maria Enriquez Negreira – the former vice-president of Spain's Technical Committee of Referees (CTA) – between 2016 and 2018.
Newspaper El Pais claimed Negreira's company – DASNIL 95 SL – produced written reports and DVD assessments of referees prior to games.
On Friday, however, Barca – who have denied any wrongdoing – were charged with corruption over alleged payments to Negreira, who is also facing charges along with the club's former presidents Josep Maria Bartomeu and Sandro Rosell.
It also emerged on Friday that prosecutors allege Barca paid €7.3m to companies owned by Negreira between 2001 and 2018.
Athletic fans jeered Barca and chanted for them to be demoted to the Segunda, and the reception left Xavi taken aback.
"I am surprised by the hostile atmosphere of San Mames and it saddens me," he said. "Judging prematurely [before a trial] is not good for society.
"Everyone is free. I respect opinions. But we are being judged prematurely, and it saddens me.
"I have nothing more to add. We haven't talked about it in the locker room.
"Those things are for the club [to deal with]. We focus on playing football, we're professionals."