John McEnroe as broadcaster talks about the crowd all the time. I only noticed this recently — maybe 30 percent of his commentary involves the crowd. A player needs to rally the crowd. The crowd has turned against someone. The struggling player should try to get the crowd going. The winning player must feed off the energy of the crowd. The crowd is into the match! The crowd really hasn’t gotten into the match! She needs to use the crowd to get to the finish line. He needs to use the crowd to stay in the match. And so on.

Hearing him focus THAT MUCH on the crowd has left me with two somewhat competing thoughts:

1. McEnroe has fallen into something of a rut as a tennis broadcaster.

2. The vitality and fire of the crowd is REALLY important in a tennis match.

Saturday’s U.S. Open Final between the legendary Serena Williams and the brilliant young Bianca Andreescu made the second case. The New York crowd, with its fury and hope, swayed the match and almost tipped it over. In the end, it took a near heroic stand from a teenager to fight them off.

The story begins at the end — Serena Williams’ end. We can all see it coming. Maybe it’s in a year. Maybe it’s in three. But you can see it through the fog, getting larger and larger with every passing anticlimax. Williams has reached the last two Wimbledon finals and, now, the last two U.S. Open finals. Each time, the celebration for her 24th major champions was decisively put on ice.

At Wimbledon last year, Angelique Kerber dominated 6-3, 6-4.

At the U.S. Open last year, Naomi Osaka dominated 6-2, 6-4.

At Wimbledon this year, Simona Halep dominated 6-2, 6-2.

It is hard to say with any certainty just how well or poorly Williams’ played in these matches. All three of the opponents — undoubtedly inspired by the moment — raised their level to previously unknown heights. Kerber was a whirlwind. Osaka hit the ball impossibly hard and with razor-sharp precision. Halep at this year’s Wimbledon chased down every ball and chased down every ball and chased down every ball. “She so speedy!” my daughter and I would shout every time Halep ran down another sure winner from Williams.

You could imagine even the young Serena Williams falling against such breathtaking play.

But, a trend is a trend is a trend: There had to be SOMETHING off about Serena Williams, right? Did she tighten up a little after winning so many ferocious battlesin her career? Does her body now wear down over two tough weeks of play? Is age — Williams turns 38 later this month — taking its inevitable toll?

The fear of Serena’s end gave Saturday’s final a palpable sense of desperation. The theme was vivid from the first ball: This HAD to be the time. Williams was playing well and looked healthy. Her opponent, meanwhile, was in her first grand slam final, this after being in her first grand slam semifinal, this after being in her first grand slam quarterfinal, this after being in her first grand slam round of 16. Yes, everything was new for Bianca Andreescu. Surely, she would wilt at least a little under the brightest lights. Surely, Williams would find her superpowers one more time in New York City.

Only, it didn’t go that way at all. Andreescu reportedly has been meditating since she was 12 years old. When she was 16, she created a pretend check that she awarded herself for winning the U.S. Open. She has done that every year since. She was ready for the moment.

And she hit Serena Williams off the court. Like her hero, Halep, she seemed to get every ball back, and Williams had no answers to a player who refused to yield. Andreescu took the first set 6-3, and she powered her way to a 5-1 lead in the second set,. She had match point. It looked for all the world like this would be one giant step forward for a 19-year-old phenom and one giant step toward the retirement for Serena Williams.

And then … the crowd took over.

Unlike the previous three final losses, there can be no question about Williams’ performance in this match: She struggled mightily. Her serve was a mess. Her groundstrokes were off. “I think this is the worst match I played all tournament,” she said, and she was right. But she’s still Serena Williams and she cracked a forehand winner to save Andreescu’s match point. The crowd went bananas. And then, Williams broke Andreescu’s serve. And the crowd went more bananas.

And then Williams held her serve to make it 5-3, and now the crowd rose to a fever pitch rarely seen in the history of tennis. They could sense something was happening. And, even more dramatically, they could sense that they were MAKING It happen. Andreescu was visibly shaken. And, sensing this, the crowd cheered madly at every Williams winner and, more directly, at every Andreescu miss. “Please!” the chair umpire pleaded with the crowd repeatedly to play fair, but there was no holding them back. They could see the miracle comeback. They could see Serena Williams holding the trophy. Andreescu was the person blocking dreams.

At one point, Andreescu put her fingers in her ears to try and shut out the crowd.

But it was no use. She lost her ability to make even the simplest shot. Serena broke her at love, and then held her own serve to make it 5-5. Andreescu was overwhelmed. There have been many famous collapses in tennis. McEnroe himself won the first two sets against Ivan Lendl and had a break in the third but lost his first serve and lost in five. And that was without the howling of the crowd roaring against him.

At 5-5, Andreescu served. Who knows what she told herself in that moment? Who knows how she calmed herself down? But somehow she did. She held a shaky serve, and when that happened, you could see everything in her body language changed. The spell had been broken. And, just like that, she broke Serena Williams, ending the match with a ferocious forehand winner down the line.

When she was asked what was the hardest thing to overcome in winning her first major championship, she laughed nervously and said, “The crowd.”

“I know you guys wanted Serena to win,” she told the crowd. “So I’m so sorry.” If you just read those words, they could sound sarcastic or a touch bitter — that’s not at all how she meant it. Andreescu was sorry to disappoint the crowd. But she has her own purpose in this game, and surely, they could understand.

Her future looks impossibly bright.

And as for Serena Williams, her future will be what she wants it to be. On most days, she still plays tennis better than any woman on earth. But the disappointments pile up. Four crushing final losses in a row. How much longer will she love tennis so much that it will be worth trying again? She is the only one that can answer the question — and it’s quite likely that even Serena herself doesn’t quite know.