The game started badly for Los Blancos as Asencio was sent off in the seventh minute after bringing down Rondon when he was left alone in front of Courtois. Despite the numerical disadvantage, Xabi Alonso's team showed character and defensive solidity in the early stages of the game.
Jude Bellingham opened the scoring in the 36th minute with a run into the box and an accurate left-footed shot.
Just before the break, Alexander-Arnold sent in a cross from the right flank that Gonzalo García fed Guler for Madrid's second goal in the 43rd minute.
In the second half, Real Madrid maintained control of the game and extended their lead in the 70th minute when Valverde converted for the third goal.
Pachuca pulled a goal back in the 80th minute when Montiel's shot from outside the box deflected off a white defender, surprising Courtois who had made several fine saves.