It was unclear as to why Byers left the rink, but Team GB had said before the competition that they would only use their permitted substitute if a player was injured or ill.
The goal was tough on the home team, who would have levelled almost instantly but for a superb block by McCarthy, who smothered a shot from Owls substitute - and former Palace player - Tom Soares.
Ronaldo, the world's most expensive player, then set up substitute Jose Callejon to complete the home scoring as Real secured their second 4-1 win of the season over Atletico.
Sully Muntari came on as a second-half substitute, seemingly confirming Mourinho's belief that the player had reduced energy levels as a result of fasting for Ramadan.
Laszlo handed 17-year-old Scott Robinson, who became the youngest player to feature in the SPL when he made a substitute appearance two seasons ago, his full debut while there was also a rare start for strike partner Jamie Mole.
The Frankfurt-born player was given his international debut by Guus Hiddink and was mainly used as a substitute at the 2002 World Cup while still a student, where his only start was in the semi-final against Germany.