Real Madrid moved three points clear at the top of LaLiga after Nacho scored the only goal in a 1-0 win over Real Valladolid at Estadio Jose Zorrilla.
With title rivals Barcelona slipping to a 2-0 defeat to Valencia on Saturday, Zidane's men earned a hard-fought victory over a Valladolid side that came into the game unbeaten in three league matches.
Chances were few and far between at either end and the points looked likely to be shared after Karim Benzema missed from point-blank range with only Valladolid goalkeeper Jordi Masip to beat.
But Nacho arrived in the box to head home with 12 minutes left and put his side in the driving seat at a crucial stage in the title race.
Valladolid's Joaquin Fernandez was lucky to escape with just a booking after a 10th-minute foul on Rodrygo and Casemiro then connected with Toni Kroos' free-kick to score with a header but the goal was ruled offside following a VAR check.
The hosts' high press forced Madrid onto the back foot and Thibaut Courtois made an acrobatic one-handed save to keep Michel's looping cross-cum-shot from dipping under the crossbar.
The Madrid goalkeeper was alert to another testing high ball 10 minutes before half-time when Raul Garcia's swerving drive from distance whipped across the face of goal, the Belgium international parrying it away from danger to keep the scoreline blank.
Rodrygo drew a good save from Masip early in the second half and Benzema should have beaten him from close range when he collected Isco's cross just before the hour mark but he fired tamely into the goalkeeper's hands.
Madrid remained patient and turned the game in the 78th minute when Kroos collected a poor clearance and floated a cross that Nacho met with a well-aimed header into the far corner of Masip's net.
Sergi Guardiola thought he had scored the equaliser when he fired high into the Madrid net from close range three minutes from time but his effort was ruled out for offside as the points went south to Madrid.
What does it mean? Nacho strike could prove crucial
With the title race shaping up to be a two-horse race, Madrid might not get many chances to open up a gap over Barcelona and Zidane will be grateful to his full-back for succeeding where his forwards failed in front of goal.
Kroos keeps his cool
With the visitors in desperate need of chances late in the game Zidane sent on Lucas Vazquez to try to add creativity but it was Kroos who came up with the killer pass to tee Nacho up for the winner.
Benzema's wait goes on
Madrid's best chance of the game fell to Benzema whose tame effort from close range was easily saved and he left the field having failed to score in his last six games for Los Blancos.
Madrid are away at Zaragoza in the Copa del Rey round of 16 on Wednesday, while Valladolid's next game sees them travel to Mallorca in LaLiga on Saturday.