Although Alexander-Arnold had already featured five times for his new club at the FIFA Club World Cup—where Madrid reached the semi-finals—this match marked his first appearance at the Santiago Bernabéu.
He received a standing ovation from the home crowd when he was substituted for Dani Carvajal in the 68th minute.
The only goal of the game came from Kylian Mbappé, who calmly converted a penalty after being brought down in the box.
The French star sent goalkeeper Sergio Herrera the wrong way to give Real a winning start to their league campaign, which also marked Xabi Alonso’s first domestic match in charge.
Real, last season’s runners-up under Carlo Ancelotti, dominated the game and created several chances to extend their lead. Defenders Dean Huijsen—making his league debut after joining from Bournemouth—and Éder Militão both tested Herrera with long-range efforts.
The match also saw debuts for £43 million left-back Álvaro Carreras, signed from Benfica, and 18-year-old Franco Mastantuono, a £38.5 million acquisition from River Plate.
Osasuna ended the match with 10 men after Abel Bretones was sent off in stoppage time for a late challenge on Gonçalo Garcia.
