In an instant, they were bewitched.
As he soared above the turf, connecting with a picture-perfect bicycle kick, they were smitten. It was a goal of jaw-dropping brilliance, combining elite athleticism with perfect technique and timing.
The Juventus fans in attendance at the Allianz Stadium stood and applauded Cristiano Ronaldo's stunning second goal. They knew it meant they were going out of the Champions League at the quarter-final stage, that their wait to be crowned kings of Europe once again would extend into a 23rd year. But sometimes, in the face of such brilliance, all you can do is stand and applaud.
Real Madrid won the first leg 3-0, but Juventus, not short of a world-class player or two of their own, fought back, levelling the tie on aggregate in the return fixture.
Enter Ronaldo. Eight minutes of stoppage time had elapsed as he began his run-up. These are the moments he lives for. A last-gasp penalty, all or nothing. He takes all.
He was the thorn in their side; he is now their rose.
That tie alone didn't convince Juventus to fork out a club-record €100million for a player who'd turn 34 during the season, making him by far the highest-paid player in Italy. It's his entire body of work: a five-time Champions League winner; a five-time Ballon d'Or winner; the Champions League's all-time leading scorer; two goals against them in the final the year before.
Juventus knew this was extreme short-termism, but they have gambled on Ronaldo being the catalyst in Massimiliano Allegri's side claiming the club's first Champions League title since 1996. The huge investment reflects Ronaldo's ability to reliably produce moments of game-defining magic when it matters most. And Juve need him to conjure something special against Atlético Madrid on Wednesday night.
Between them, Juventus and Atlético have been the beaten Champions League finalists in four of the last five seasons. With Real Madrid, reigning champions for the last three years running, eliminated by Ajax last week, and with 2015 winners Barcelona looking far from their impervious best, both will see this year as their best opportunity to get over the hump.
And it was Alteli who drew first blood, winning 2-0 in the first leg of their last-16 encounter at the Wanda Metropolitano three weeks ago.
Diego Simeone's side have been among Ronaldo's favourite opponents in his career. He is the record scorer in Madrid derbies and, with 22 goals and eight assists against Los Colchoneros, he has been directly involved in more goals versus Atlético than any other opponent he's faced. But he was well marshalled by Diego Godín and José Giménez at the Wanda this time, largely kept quiet.
As expected, Ronaldo took little time to settle in Serie A. He is currently the division's second-highest scorer, with 19 goals from 25 starts, and has demonstrated a surprising unselfishness in providing eight assists.
The Atlético reverse began a run of three fixtures in which Ronaldo has failed to score or assist, and he has found scoring opportunities a little harder to come by in recent months, his expected goals per 90 minutes more than halving to 0.42 from mid-November, where before it had been up at 0.94.
There is no doubt that he remains Juventus' key man, though, and in the three games before his present dry patch, he scored four and assisted three.
With Ronaldo on board, having been Serie A champions for the last seven consecutive seasons, Juventus have gone from merely dominant to unbeatable, yet to taste defeat in 27 games, dropping only six points.
His presence will mean they do so in more spectacular style, almost certain to set a new record for points accumulated in a single season, but Juventus didn't sign Ronaldo to protect their dominion over the Italian top flight – they would likely have won Serie A again anyway, Ronaldo or no Ronaldo.
It is the club's performance in the Champions League during his time there that Juve's decision to invest so heavily in an ageing superstar will be judged.
It doesn't have to be a spectacular bicycle kick. It doesn't have to be a 98th-minute penalty. But Juventus need Ronaldo to be decisive against Atlético. They need him to be the hero they fell for.