Dembele, who has been heavily linked with a move to Paris Saint-Germain in recent days, scored against the run of play with a fine shot across Thibaut Courtois to give his side an early lead.
Real Madrid looked to have an almost immediate route back into the game after Ronald Araujo was judged to have handled the ball in the area, but Vinicius Junior struck the subsequent penalty kick against the bar.
It was to be the straight of a string of unfortunate events for Madrid, who hit the bar, post and saw an effort cleared off the line in a frantic and fiery first half.
It was more of the same after the break as Aurelien Tchouameni and Jude Bellingham both went close – the first a powerful effort from the edge of the area and the second a neat header from 10 yards – but Madrid just could not breach Barca’s back line.
Vinicius went closest after carving open a space inside the area five minutes from time, but could only bend his shot an inch around the post. Minutes later, it was 2-0 to Barcelona as Fermin Marin capitalised on abysmal defending to drill home from the edge of the area.
Five minutes later and Ferran Torres got a toe on the ball ahead of Courtois to slot into an empty net for a third as the Texas crowd were treat to late drama – and eight yellow cards!
