Former Chelsea striker Diego Costa scored four goals and was sent off as Real were embarrassed in New Jersey.
Joao Felix, a big-money summer signing from Benfica, scored his first Atletico goal before Real made a belated comeback from 6-0 down.
‘I’m not concerned, but I’m hurt,’ Real manager Zidane said at his post-match press conference, reported on the club’s official website.
‘You don’t play to lose. But we can’t be looking backwards.