The match resumed.
Slaven Bilic, seeing his moment, waved his arm, ordering his team into a frenzied press to exploit any confusion from the substitution.
But United, now 2-0 up, simply sank into their classic Mourinho defensive shell.
Lukaku dropped back, and Ling and Mkhitaryan tucked inside, forming a flat, compact, four-man midfield line.
Suddenly, Old Trafford was a fortress of red shirts.
West Ham had the ball, but they were mired in difficulty, passing it uselessly in front of an impenetrable wall.
"We can see Ling's movement is very active," Zhan Jun noted.
"He's already dropped back, compensating for his defensive shortcomings with pure work rate."
Suddenly, Matic, a long leg shooting out, made a beautiful, clean tackle and immediately passed the ball to the left flank.
Ling's heart pounded.
His first touch in the Premier League.
He received the pass and quickly scanned the field, but before he could even think about turning, Pablo Zabaleta was thundering in from behind, giving him no space.
'A rookie,' Zabaleta thought, his eyes narrowing.
He still had a bitter taste in his mouth from that pre-season friendly, that hot-headed Chinese kid from Bremen, Zhang Yuning.
'These young kids are all the same. No composure.'
With his years of experience, dispossessing a debutant should be easy.
He lunged, expecting the rookie to panic.
Seeing the breakthrough had vanished, Ling didn't force it.
He calmly, safely, played a one-touch pass back to Matic.
"Smart!" Zhan Jun exclaimed in the broadcast booth. "Very smart. His first touch in the Premier League, under pressure from a legend like Zabaleta, and he doesn't try to be a hero. He keeps possession. That's maturity."
Only 5 minutes remained in regular time.
West Ham, unable to get the ball, grew increasingly anxious and pushed high up the pitch, leaving massive gaps.
The ball returned to Matic.
He spotted Paul Pogba in a pocket of space.
Pogba received the pass.
"Why isn't he releasing the ball?!" Zhan Jun almost shouted, as three West Ham players closed in.
But Pogba, ever the performer, waited.
He invited the press.
He drew them in.
He waited for Zabaleta to get sucked inside.
He waited until he saw the white blur of Ling's shirt on the far-left flank, all alone.
Then, just as the trap was about to close, Pogba swung his calf, launching a brilliant, 60-yard cross-field pass.
It was a rainbow, soaring over everyone's head, landing perfectly in front of Ling, who had acres of space.
Ling calmly controlled the ball, took one look, and abruptly accelerated, driving straight at the byline.
He felt as if his soul had left his body, teetering on the edge of extreme calm and pure exhilaration.
Zabaleta, realizing he'd been tricked, scrambled, cutting diagonally toward the penalty area.
In the blink of an eye, Ling was at the edge of the box.
West Ham's defenders were scrambling to mark Lukaku and Mkhitaryan.
A breakthrough was needed.
Ling gradually slowed his pace, his right foot tapping the ball, inviting the challenge.
Zabaleta stood firm, bracing for the tackle.
'This kid thinks he can get past me?' Zabaleta thought, almost laughing.
'Back in the Argentine national team, even Messi can't beat me 1-on-1 every time. Who do you think you are?'
On the sidelines, Mourinho leaned forward, his eyes locked on Ling.
'Come on, kid,' he thought. 'Prove it. Show them.'
Not far behind the West Ham bench, a young substitute, Declan Rice, sat bolt upright, his breathing suddenly rapid.
The distance between the two players narrowed.
Ling tuned out the chaotic noise, slipping into the same pure focus he had during his cone drills.
He made his move.
The Matthews Shoulder Drop.
His upper body feinted hard to the right, a violent, sudden sway.
Zabaleta, the world-class defender, reacted.
His hips, his center of gravity, his entire body—all shifted to block the inside cut.
But it was a ghost.
Ling's weight was already on his left foot.
In that split-second of imbalance, as Zabaleta's feet were planted in the turf, Ling was gone.
He didn't just cut inside; he exploded past the veteran's desperate, lunging leg, leaving him for dead.
Joe Hart, seeing the move, scrambled to shift his position, his eyes wide with panic.
He didn't want to be the punchline again.
Old Trafford held its breath.
Lukaku, free in the center, let out a boisterous shout: "Here! Here! Here!"
Ling, of course, heard him.
His head was up.
Under Joe Hart's desperate gaze, the young #23, in on goal, calmly and unselfishly played a perfect cutback pass.
Lukaku muscled off his marker and gleefully slotted the ball into the empty net.
He may be the poster boy for "joyful football," but he wasn't going to miss that.
3-0!
WHOOOOOOSH!
The sound that erupted from Old Trafford was almost tangible, an ear-splitting wave of pure joy.
Tens of thousands of fans in the Stretford End, the Sir Alex Ferguson Stand, all of them... they rose to their feet, trembling with excitement, wildly waving their arms.
"Who is that young man?!" a fan shouted to his friend.
"Number 23? Is he Korean? Are we getting another Park Ji-Sung?!"
A group of fans nearby, with black hair and yellow skin, glanced at each other, their faces filled with an emotion they hadn't felt in years.
One of them turned, his voice thick with pride.
"No," he said, puffing out his chest. "Like us, he's Chinese!"