The moment the teams stepped out of the tunnel, the world dissolved into a dizzying kaleidoscope of color and a deafening wall of sound.
The San Siro, shared by both clubs, was a beast of two hearts tonight.
One half was a roaring sea of AC Milan's red and black, the Curva Sud, a fortress of flags and flares.
The other half was Inter's Curva Nord, a pulsating wave of blue and black, equally loud, equally passionate. The noise was so intense it felt like you could breathe it in.
On the pitch, the pre-match handshakes were a tense affair. Theo Hernández, Milan's fiery left-back, shared a brief, intense stare with Inter's Denzel Dumfries, a promise of the physical battle to come.
In the center circle, Lautaro Martínez and his Milan counterpart, Davide Calabria, exchanged a firm, respectful handshake, the calm in the eye of the storm.
Leon found himself near Mohammed Kudus.
The Ghanaian winger was bouncing on the balls of his feet, a bundle of kinetic energy.
"Big crowd tonight," Kudus said with a wide, confident grin, his voice almost swallowed by the noise.
"It's the Derby," Leon replied with a small smile. "It's always big."
"Good luck," Kudus said, though his eyes sparkled with a competitive fire that said, 'You're going to need it.'
On the sidelines, Coach Chivu was in a low, intense conversation with his assistant. "Watch Simons," he muttered, his eyes fixed on the young Dutchman. "He's their brain. If we cut him off, their body will freeze."
Across the technical area, Milan's coach was doing the same, pointing at Leon. "He's not on the wing! He's floating. Don't let the defenders get dragged out of position. Midfielders, you must track him!"
The referee placed the ball on the center spot. The stadium's roar crescendoed into a single, deafening shriek of anticipation. The whistle blew. The Derby della Madonnina was underway.
From the very first second, the game was played at a blistering pace.
AC Milan, fueled by their home crowd, came out swinging. And at the heart of it all was Xavi Simons.
The conductor's baton symbol above his head was glowing brightly in Leon's Vision. Simons demanded the ball, switching play with effortless grace, his passes crisp and intelligent.
Leon, meanwhile, began to play his part as the ghost.
He started high, right between Milan's two central defenders, Fikayo Tomori and Malick Thiaw.
But as soon as the ball moved into the midfield, he would drop, drifting into the pocket of space Chivu had described.
In the 5th minute, the tactic almost paid off. Leon dropped deep, pulling Tomori a few crucial yards forward. Instantly, Lautaro darted into the space behind him.
Leon, without looking, flicked a pass into the channel.
It was a move straight from the training ground. But Tomori, a defender with incredible recovery speed, managed to get back just in time to make a last-ditch tackle.
The game was a frantic, high-stakes chess match.
Leon's Vision was working overtime. He saw the conductor's baton flash above Simons' head just before he attempted a clever through-ball, allowing Leon to intercept.
A moment later, Leon saw a sprinting feet symbol on Kudus and shouted a warning to Dimarco just as the winger began a dangerous run.
In the 18th minute, Kudus showed why he was so feared. Receiving the ball on the right wing, he faced his defender.
His Vision stats flashed in Leon's mind: [Dribbling: 90].
With a dizzying series of step-overs, he exploded past his man, cutting inside. Barella came across to cover, but Kudus dropped his shoulder, shimmied to the left, and was past him too.
He was a blur of red and black, heading directly for the penalty area.
Stefan de Vrij, Inter's experienced center-back, saw the danger.
He had no choice. He lunged in, not to win the ball, but to trip Kudus, sending him tumbling to the grass.
The referee's whistle was immediate. A clear yellow card. The Milan fans screamed for red, but it was a fair call.
The intensity was ratcheting up.
Tackles were flying in, and the referee was struggling to keep a lid on the simmering aggression.
Then, in the 29th minute, the game was turned on its head.
The ball was loose in the center of the park. Nicolò Barella, Inter's tenacious engine, lunged for it.
At the exact same moment, Milan's midfielder, Ismaël Bennacer, came flying in from the other side. Barella got his foot to the ball first, poking it away. Bennacer was a fraction of a second late, but he didn't pull out of the challenge. He came in high, his studs catching Barella square on the shin.
It was a horrible tackle. A collective gasp went through the stadium. Barella writhed on the ground in pain. The Inter players were furious, surrounding the referee. But the official needed no convincing. He ran straight to Bennacer, his face grim, and brandished a straight red card.
The Milan players and fans were stunned into silence, which quickly turned to rage. Bennacer protested his innocence, but the decision was made. AC Milan were down to ten men.
With a man advantage, Inter seized control. The chaos Leon was meant to create with his movement was now amplified by the chaos of Milan's numerical disadvantage.
The red and black shirts were scrambling, trying to plug the gaps.
In the 38th minute, Inter constructed a beautiful passing move. The ball moved from Barella to Leon, who had dropped deep again. He turned, surveyed the pitch, and saw Cole Palmer making a darting run from the left wing into the box.
A winding arrow symbol confirmed his path.
Leon threaded a perfect pass through the disorganized Milan defense, right into Palmer's path.
Palmer took one touch to control it.
The goal was at his mercy. He was about to shoot when Fikayo Tomori, in a desperate attempt to save his team, launched into a reckless sliding tackle from behind. He didn't get the ball.
He only got Palmer, who went down in a heap.
The referee didn't hesitate for a second. He pointed directly to the penalty spot.
The San Siro erupted. The Inter fans were delirious with joy; the Milan fans were incandescent with fury, their jeers and whistles reaching a fever pitch.
As the Milan players crowded the referee to protest, Lautaro Martínez calmly walked over, picked up the ball, and placed it on the penalty spot.
As captain, the responsibility was his. He spun the ball in his hands, his face a mask of pure, unshakeable focus.
The weight of the Derby, the chance to take the lead against their ten-man rivals, rested squarely on his shoulders.
He took a few steps back, his eyes locked on the Milan goalkeeper, Mike Maignan.
The stadium held its breath. The 40th minute was on the clock.
The world seemed to shrink to just these two men, separated by twelve yards.