Los Blancos rallied in the second half as Carlos Espi's first goal for the club secured a victory with several key names still absent from Josee Mourinho's squad.
Kylian Mbappe and Jude Bellingham are among those due back in training next week following an extended break after the 2026 FIFA World Cup.
Mourinho will need to tailor his plans for the start of the 2026/27 LaLiga season and captain Fede Valverde admitted the Portuguese coach's trademark ruthless approach has been well received on his return to Madrid.
"He's very approachable. He has a tough personality, but I think that's the way he can best connect with you.
"I like how he treats the team and how he treats me. I'm happy and, as captain, I try to give my best so that my teammates and the coaching staff feel comfortable with us, and we with them.
"We're continuing to refine what the coach wants, the ideas he wants from the team. There are still many players missing, but we're finding our rhythm."