Francesco Totti scored a fine second-half goal at the Cotton Bowl in Texas to see the Serie A giants to their first win of the pre-season tournament.
Real – beaten by Inter in their opening game – had their chances, particularly during the first half, but failed to capitalise and were punished by Totti as their defence of the trophy was ended.
Things threatened to boil over even before kick-off after Roma midfielder Seydou Keita, formerly of Barcelona, refused to shake Pepe's hand and then threw a water bottle at the Real defender.
Real started the better of the two teams when the clash started with Gareth Bale particularly impressive, causing problems down the left.
It was unsurprisingly Bale for whom the game's first real chance fell in the 20th minute.
A fine team move led to a cross from Lucas Vazquez for Bale, but the attacker could only slice his shot well wide under heavy pressure.
Roma looked most threatening on the counter-attack and when Totti was on the ball as Bale continued to cause them problems, shooting over from the edge of the area.
Luka Modric was heavily involved throughout and combined well with Bale on several occasions, but Carlo Ancelotti's men would somehow fail to score in the opening half.
Winger Vazquez forced Lukasz Skorupski into a save after a volley from inside the area and Mehdi Benatia made a brilliant block to deny Pepe on the follow up just before the break.
It would be Roma who took the lead in the 58th minute thanks to Totti.
Totti dummied a pass that found Alessandro Florenzi's overlapping run down the right before continuing his run to put the cross away and into the bottom corner from near the penalty spot.
Substitutions ruined the flow of the game, but Roma were largely untroubled on their way to victory despite a sequence of late pitch invasions which featured multiple intrusions.
