The stadium rose with applause when Trent Alexander-Arnold, the former Liverpool right-back, was taken off during his La Liga debut - but Real Madrid fans were actually cheering Dani Carvajal.
The 26-year-old ended his 20-year stint with the Reds last season before his contract was set to expire at the end of June. Real Madrid shelled out around $13 million (£10 million) to the Reds for his early release, enabling him to play in the Club World Cup across the United States.
Alexander-Arnold played in several matches but was absent from Real Madrid's 4-0 semi-final loss to PSG in New Jersey due to injury. The England international made his first La Liga start in Tuesday's 1-0 victory over Osasuna.
He was replaced in the 68th minute as the entire Santiago Bernabeu stood up to welcome Dani Carvajal, who was making his first appearance for Los Blancos in nearly a year after recovering from an ACL injury.
After the match, the former Reds full-back shared a message on Instagram, writing: "Incredible sensation to play in my new home. Excellent way to begin the season with a victory."
He included a series of photos in the post and was clearly delighted to be involved. But with Carvajal back in action, Alexander-Arnold now faces increased competition for a starting position.
Before the match, pundit Javier Herraez suggested that the Englishman is 'nowhere near' the level he demonstrated during his time at Anfield.
"I'm waiting for Trent," he told Cadena SER. "He's come to play, but I don't see him in good shape. I've always liked watching the Premier League, watching this player. He's better going forward than in defence, that's more than obvious.
"He's more of a wing player in a three-man defence than in a four-man defence. That's where it's hard for him to get deep. Trent has a month to get sharp, because if he doesn't, Carvajal will eat him alive.
This article contains affiliate links, we will receive a commission on any sales we generate from it. Learn more
"But come on, it's a piece of cake. That's what I think based on what I saw at the Club World Cup and the friendly. Trent is nowhere near the Liverpool player. Maybe it's pre-season, but I haven't seen him well."
As Alexander-Arnold was playing, Mohamed Salah won the PFA Player of the Year award for a third time. And he sent the Egyptian a message on Instagram.
Alexander-Arnold shared a picture of Salah on his social media story. He added an emoji of a crown and the word "History".
Liverpool.com says: Alexander-Arnold should do well at Real Madrid but the fans love Carvajal. If he doesn't play well straight away, there will be a big clamor to get the Spaniard back in the starting XI.