“It’s just a number,” Mariano Díaz said. But it isn’t. Over on the touchline, the fourth official held up the board. Coming off: No 11. Coming on: No 7. Mariano stood and waited for Gareth Bale, wearing the shirt Cristiano Ronaldo wore for eight of the nine years he spent at Real Madrid until his departure this summer, that Raúl González Blanco wore for the 16 years before that and Emilio Butragueño wore for the 12 years before that.

Thirty-six years, 14 league titles, seven European Cups and 911 goals later, it was his. No pressure. As he waited, Julen Lopetegui approached. “I told him to stick it in the top corner,” the manager said jokingly. “And he did what I said.”

In the dying minutes against Roma on Wednesday, Mariano smashed a shot that tore past Robin Olsen. He had been a Real player for 19 minutes. Well, 19 minutes and six years. At 25, this was a “re-debut”. “I’m super-happy,” he said.

Born in Premia de Mar in Catalonia, he watched Ronaldo, the Brazilian, and Ronaldinho and Samuel Eto’o when he was growing up. He joined Real from third-tier Badalona in 2011, playing for Real C and then their second team, Castilla. His manager there was Zinedine Zidane – and it was Zidane who intervened when his contract was running down, with only six months left and little sign that he would continue. Six months later, he was in the first-team squad. I in 2016-17 he played 14 games, scoring five times.

Apart from the Copa del Rey, opportunities remained limited and, having played only 115 minutes in the league, he was sold to Lyon at the end of the season for €8m. He did not want to go. “If Zidane had said he was counting on me, I would have listened for sure,” he said – but Madrid convinced him.

On a night when Real Madrid's old #7 dominated the headlines...



Real Madrid's new #7 made some of his own!



Mariano Diaz take a bow 👌 pic.twitter.com/km1ousbHuH — Football on BT Sport (@btsportfootball) September 19, 2018

A year and 21 goals later, he was ready to return to Spain, a deal agreed with Sevilla for €35m. Real, who were owed 35%, had the option to match any bid and, after the departure of Ronaldo, Lopetegui was pushing for a striker. Reports suggested the striker had turned Real down but Mariano publicly announced: “You can’t say no to Real Madrid.” Furious, Sevilla saw him slip through their fingers. “I hope they understand,” Mariano said. Real forfeited the share they would have received and paid the remaining 65%, €22.75m, to bring Mariano back, presenting him with his new shirt at the end of August.

“The kit man asked which shirt I wanted and I said seven,” he said. “It’s the one that was free, I imagine no one wanted it.”

Mariano, who has a Dominican father, scored for their national team against Haiti in March 2013 but has decided not to continue in the hope of playing for Spain. “I’d love to play for Spain; I’m going to work so that one day Lopetegui calls me,” he told El País in November last year.

Lopetegui was then Spain’s manager; by the time the call came this summer, he was the manager of Real. “I was super-nervous when he rang,” Mariano said but the conversation was convincing; Lopetegui told Mariano that despite the players ahead of him, he would get opportunities.

The first did not come until Wednesday, and there was a touch of impatience from some. Real’s play had improved but some felt they lacked a predator to make it pay. A youth teamer returning home, when Mariano went to warm up there was a huge cheer and another accompanied him on to the pitch. He ran straight at Roma, showing no sign of pressure. There was a directness, a bluntness about his response to the shirt that fits the way he plays – even if, pushed, he insisted: “I have a lot, a lot, of respect for Ronaldo and everything he has done, and for all those who have worn this shirt.”

Ronaldo, Raúl and Butragueno have been the previous occupants but if there is a Real player that comes to mind watching him, it may be Hugo Sánchez, the forward who one season scored 38 league goals, all with a single touch: strong, quick, direct, aggressive, a finisher. No messing, just goals.

Marcelo joins in the celebrations after Mariano Díaz’s goal. Photograph: Quality Sport Images/Getty Images

Mariano had taken eight shots as a Real player and scored from five, according to Opta; it is six from nine now. There is something about him that recalls Bill Shankly’s remark to Ian St John: “If you’re not sure what to do with the ball, just pop it in the net and we’ll discuss your options afterwards.”

Only Mariano is not likely to “pop” the ball anywhere; he is more likely to bludgeon it. He certainly did against Roma, sending it flying into the net. “I’m going to keep this shirt for ever,” he said.