Mbappe's goal from the penalty spot guided Real Madrid to make a winning start to their LaLiga campaign at the Bernabeu.
Xabi Alonso's men, who dominated the game from start to finish, overcame Osasuna 1-0 on the opening matchday of the season.
After a goalless first half, Mbappe, last season's Golden Boot winner, gave the Madridistas the win with a penalty goal early in the second half of the clash. Carreras, who started the game, and Mastantuono made their official debuts for the team, Real Madrid reports.
Madrid started on top and pressed high up the pitch. Carreras was the first to try his luck with a long-range left-footed effort that went just wide (7'). Ten minutes later, Huijsen also attempted a shot from outside the area, but Sergio Herrera deftly pushed his effort wide.