With Thibaut Courtois, Federico Valverde, and Kylian Mbappé all given the night off by Carlo Ancelotti, it perhaps wasn’t surprising to see Real Madrid make a slow start.
Takefusa Kubo set out to punish his former employers, playing a smart one-two with Brais Méndez before rifling a shot at the near post that was beaten away by Andriy Lunin.
Sociedad’s bright start ultimately failed to bear fruit, and Los Blancos punished them in trademark fashion on the counter-attack.
Jude Bellingham’s pinpoint long ball was brilliantly controlled by Endrick, allowing him to use his second touch to drive an outside-of-the-boot shot along the turf past a helpless Álex Remiro for his fourth Copa goal of the season.
Undeterred, Imanol Alguacil’s men plotted a comeback route, but Lunin was equal to efforts from Méndez and Mikel Oyarzabal in quick succession.
The visitors’ threat on the break – charged by Bellingham – was substantial, and Madrid came close to doubling their lead on the half-hour when the Englishman slotted through Vinícius Júnior, but he was denied by a brilliant Remiro save.
There was still time for Ander Barrenetxea to draw a brilliant save from Lunin before the break, with stoppage time extended as the game was paused by the referee in response to the grotesque nature of chants from the crowd.
There were chances at both ends as order resumed after the break, with Oyarzabal’s close-range header smothered by Lunin before Endrick rifled an effort against the Sociedad crossbar.
Half-time substitute Lucas Vázquez was next to go close as he cut in from the right and fired over, but the atmosphere inside the Reale Arena was increasingly subdued as the hosts failed to string together much going the other way.
The home side were indebted to a fine reflex save from Remiro for keeping their deficit at one in the final 10 minutes, as the goalkeeper brilliantly adjusted to keep out Bellingham’s shot, which had taken a wicked deflection.
Sociedad simply never got going after the break, and as a result, their Copa progress hinges on winning at the Bernabéu, which they did en route to lifting the trophy back in 2019/20 under Imanol.
Madrid, meanwhile, are now unbeaten in seven matches across all competitions as they hunt down a 21st success in this competition.