The former Liverpool player’s inclusion in midfield was largely circumstantial, with suspensions for Eduardo Camavinga, Arda Guler and Bernardo Silva leaving Mourinho short on options.
Alexander-Arnold lined up alongside Federico Valverde but had a mixed evening, creating two chances and attempting more crosses than any other Real player – but failing to win a tackle. His passing accuracy was also down at 83.3%.
He was substituted shortly after Inter pulled one back on 77 minutes, prompting whistles around the stadium – although this could well have been frustration Madrid supporters felt at their team’s performance rather than at Alexander-Arnold individually.
It was the first competitive match in which Alexander-Arnold and fellow right-back Denzel Dumfries had started together. He started both for a pre-season friendly against Fiorentina, with Alexander-Arnold operating at right-back while Dumfries played further forward on the same side.
It is clear Mourinho still doesn’t have a definite starting right-back, so in the same way Alexander-Arnold had to fight to start with Dani Carvajal last season, he is doing the same this season with Dumfries.
But BBC Sport understands the Portuguese has been impressed by the England international’s performances, values and the versatility he brings to the squad.
Indeed, Mourinho views Alexander-Arnold as different from many traditional full-backs because of his ability to move into central areas and contribute to attacks from midfield positions.
His passing, crossing, through balls and set-piece delivery remain among the strongest parts of his game.