With Sergio Ramos rested, the reigning European champion’s defense seemed disjointed and it conceded as early as the second minute when CSKA’s Nikola Vlasic intercepted a pass from Toni Kroos and struck the ball low past Keylor Navas.
Madrid slowly found its way into the game but had to contend with a tightly packed CSKA defense. Casemiro hit the post in the 28th minute with a speculative shot, Karim Benzema headed onto the bar in the 40th, and Mariano Diaz headed onto the post late on.
Even with nearly 70 percent possession and Luka Modric introduced off the bench, Real couldn’t break down CSKA and offered the Russian team chances on the counterattack.
When Dani Carvajal limped off just before halftime, Madrid seemed set to add to an injury list which already contains Gareth Bale, Marcelo and Isco.
Roma beat Viktoria Plzen 5-0 on an Edin Dzeko hat trick in Tuesday’s other game in Group G. That leaves CSKA top of the group with four points, ahead of Madrid and Roma with three each and Plzen on one point.