The buzz that had been building and building all day was now dead. As the late-afternoon shadow moved over the Grandstand court, a dark cloud seemed to suddenly loom over the match.

The whispers could be heard around the stadium: “Is he going to retire?” “Juan doesn’t look so good.” “Ay, dios mio!”

Juan Martin del Potro looked like a walking zombie. He sulked through points with little power behind his usually thunderous strokes. He crouched over, hands on his knees, at the baseline, peering off into the distance. He – a couple of times – looked as though he was going to be sick right there on the court.

Related: Day 8 Recap - Delpo's Day

“There’s no way he can keep going,” came the reverberations.

What was billed to be the outer-court match of the tournament was suddenly a grand dud. Dominic Thiem had the first set in hand, 6-1 in 33 minutes. The second? 6-2 in 34 minutes.

As the Grandstand emcee, it’s my job to be courtside for matches on my court to keep up with what’s going on and be ready for the on-court interview post-match. This one was the battle that all of my friends in the tennis media had messaged me about, “You have Delpo-Thiem?!” “Wow!” “It’s going to be incredible.”

It felt, instead, like a funeral. I stood silently disappointed, not because I wanted del Potro to win, but because we all wanted a good match. We wanted an epic.

The word was that del Potro was continuing on only for the 8,000-plus fans who had crowded into Grandstand to watch he and Thiem duke it out, a match that almost certainly would have been an Arthur Ashe shoo-in had it not been a day that also included Rafael Nadal and Roger Federer on the docket.

He was sick – had been for a couple of days leading into the match – and he was only doing what he thought to be the right thing to do. He just wanted to be polite. He didn’t want to quit. That’s not what Juan does.

But then del Potro broke serve for the first time all day to begin the third set. He sat down in a chair just on the side of the court and made eye contact with former player and ESPN analyst Mardy Fish, seated only a few feet away. Fish’s eyes widened, looking surprised. Del Potro just softly smiled.

He’d win that set 6-2, and suddenly the whispers of sorrow and disappointment turned to that of hope. Could he? Would he?

play video Del Potro vs. Thiem

That’s when the atmosphere inside Grandstand took on a life of its own. The crowd was already completely behind the 2009 US Open champion, but now they had reason to cheer other than pride.

The “Vamos! Vamos!” cries grew louder with each crunching forehand off of del Potro's racquet, as did the “Olé Olé Olé Olé! Delpo… Delpo!” chants, which stretched on and on, reverberating and growing in their intensity. And then the elongated “Delpooooooo!”

Del Potro had been out on Grandstand for two of his previous matches during this US Open fortnight, both of which were packed, with fervent fans sitting on the edge of their seats screaming his name and willing him on.

The Argentine has always been a fan favorite here and anywhere that he plays, but Monday night was different. It was a soccer match in which a ragged home team was down 4-0 at halftime and were two men shy of 11, its loyal fans only hoping for a second-half goal just to save face. One goal.

Something. Anything.

Tennis matches usually take on a story and this one began to feel like a fairy tale – at least if you were among those inside Grandstand cheering on del Potro. Here’s the favorite, beloved in tennis, seemingly not only down and out but sick and sullen on top of it.

As I stood courtside – waiting, if I was needed, to do a post-match on-court interview – I watched as del Potro saved not one but two match points on his serve in the 12th game of the fourth set. When he held his serve two points later, the crowd roared and he turned to them and roared back.

In that moment, the match was seemingly his.

In the seventh game of the final set he came back from love-40 down on serve, Thiem looking over at his camp – including his stone-faced coach Gunter Bresnik – in exasperation. “How is this happening?” said his eyes.

And when the match finished, the entire place shook. Fans in Argentina colors hugged on another. I’m almost certain there were a few tears. Del Potro stood, center court, his arms aloft overhead as he was showered in complete praise. I couldn’t hear myself holler into the microphone, “Ladies and gentlemen! Juan Martin del Potrooooo!”

This was one for the ages and everyone knew it.

“I think I deserve the trophy,” he joked in his post-match interview. The crowd laughed but everyone agreed, “Si. Si.”

As del Potro made his way from Grandstand to Arthur Ashe Stadium, flocked by security, he was followed like a beloved rock star or favorite politician. Cameras flashing. Voices screaming.

He stopped just outside of Ashe, signed a few autographs and then waved good-bye as he was whisked inside. It was an anticipated classic that lived up to its billing. In fact, you could have never written it the way it panned out before.

“It’s a good night,” he had said a few minutes earlier to his fans in Spanish on court. “I will always remember this match.”

So will we, Juan Martin. So will we.