Real Madrid established a three-point cushion at the top of La Liga after they defeated Real Valladolid 1-0 on Sunday.
Nacho Fernandez rose highest to head the travelling team in front after 78 minutes, with Valladolid having succeeded in keeping their guests at bay until deep in the latter stages.
Real moved back to the standings summit after Quique Setien's Barcelona suffered a surprise 2-0 defeat away to Valencia on Saturday.
This is the first time since October that Los Blancos have held an outright lead in La Liga, an advantage coach Zinedine Zidane won't want to give up again between now and the end of the campaign.
Zidane made several changes to the team that beat Sevilla 2-1 in Real's last league outing, with Raphael Varane the only member of the defence to survive the transition.
Nacho started in place of suspended right-back Dani Carvajal, while Sergio Ramos returned in central defence and Ferland Mendy replaced Marcelo at left-back.
Karim Benzema also came back into the team's starting league lineup, hoping to have an impact after he scored when these teams drew 1-1 at the Santiago Bernabeu in August.
Eighty-two minutes had passed before the first goal was scored on that occasion, and a tetchy first 45 minutes on Sunday suggested fans could be in for a similar wait this time around.
Visiting Real predictably assumed control of possession, but finding space in front of the Valladolid goal proved a far more complicated task.
The Spanish Football Podcast attested to a dull first half:
Sergi Guardiola—who also scored in that August clash—and Enes Unal were the top two in attack for the hosts, though the latter would often drop back to help in their defensive plight.
Real's endeavour improved after the break, but the increase in goalmouth action also led to more frustration as they sought the opener, per the Independent's Dermot Corrigan:
Nacho followed team-mate Luka Modric and Varane into the book after 76 minutes, but the defender was fully absolved of any blame moments later when he broke the deadlock.
Toni Kroos' corner was cleared out of Valladolid's box at the first attempt, but the German found the head of Nacho with his second swing in, via Premier Sports and beIN Sports (UK and U.S. viewers only):
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GOAL FOR REAL MADRID! ⚪️ Los Blancos finally get a breakthrough as Nacho Fernandez scores from a header that puts Zinedine Zidane's men top of the @LaLigaEN for the moment! #RealValladolidRealMadrid LIVE NOW ⬇️ 📺 beIN SPORTS 💻📱CONNECT https://t.co/LRYa03w6yI https://t.co/7Jo7Y2ziMd
As was the case at the Bernabeu, Guardiola put the ball in the back of the opposite net minutes later, except this time his equalising intervention was disallowed for offside.
A tense end to the match served as testament to the fine work of Valladolid, who sit 16th in the standings but played far above their status considering the opposition.
Zidane's third successive win in all competitions gives Real the breathing space they've been craving at the pinnacle, with stand-in star Nacho rising as their hero of the moment.
Real Madrid switch their focus to the Copa del Rey as they prepare to face second-tier Real Zaragoza in the round of 16 on Wednesday, while Valladolid are on the road to Mallorca in La Liga on Saturday.