Novak Djokovic looked puzzled.

He is not someone who is accustomed to being puzzled.

When you have been on tour for over 20 years, played 1,346 matches at ATP level, and won 24 grand slam singles titles and an Olympic gold, there are not many situations that you haven’t encountered before.

But there was a problem facing him from across the court that he seemingly had no answer to.

It was quite a sizeable problem — 211cm tall and 100kg, to be exact.

Reilly Opelka — from the small Michigan town of St Joseph — was playing the match of his life, hammering cross-court winners with impunity, serving like a dream.

His straight-sets 7-6 (8/6), 6-3 victory in the quarterfinal of the Brisbane International — in front of a stunned 5,500-capacity crowd — was a surprise to everyone.

On court, Opelka is simply enormous, a giant hulking figure of a man, stalking across the baseline, with a huge bushy beard under a peak cap adding to the optical sense that you are looking at something unusual and unexpected on the court.

As he lopes to his chair, his size becomes even more apparent, towering a full head taller than Djokovic.

Their post-match hug at the net looked more like WWE than a fair fight sporting encounter.

He is just wildly oversized, a colossal figure who can exact pace and bounce with every powerful swing of his racquet.

And it had Djokovic in a complete quandary.

The Serbian is arguably the greatest returner of a tennis ball who has ever lived, and has never had issues with tall players.

Granted, Ivo Karlović held a 2-1 winning record over Djokovic, although the only other player of comparable height to those two 211cm giants — John Isner (208cm) — lost 10 and won just twice.

But against Opelka, all those years of experience, all those countless moments of adversity counted for nothing.

The greatest player who has ever lived simply couldn’t lay a racquet on his opponent’s groundstrokes.

Opelka whacked a phenomenal 36 winners in the match, getting 77 per cent of his first serves in and winning 78 per cent of those points.

In the first set, he was even better, serving at 83 per cent and winning all six of his points on the second serve.

Djokovic did not play badly. Not by a long shot.

Opelka just played better.

“He’s the greatest tennis player the sport has ever seen,” Opelka said of Djokovic.

“You know, it’s difficult being in Novak’s position.

“He can scout me or his other opponents all day long.

“The reality is we have nothing to lose coming in against him.

“He’s the greatest forever, so you end up playing more free and you do things, you take a lot more risks because it’s your only chance.

“If you play your normal level or even above a normal level, he’s gonna win every time.

“So it’s tough in his position because he gets guys that are good players, that roll the dice and on a day like this, when a lot of things go my way, you know, that’s how it works out.”

Opelka proved his worth throughout the match, as little by little the capacity crowd realised that the script was being re-written by the most unlikely of figures in front of their eyes.

His serving was astonishing, but more impressive were his forehand winners, creating angles that had Djokovic scrambling and reaching and stumbling out wide, unable to get even a touch.

His nerve was tested by serving out the match, something he did in such deadpan fashion that it looked like he was finishing a warm-up.

“You know, I just focused on my spots,” Opelka said.

“If I hit ’em, it’s hard to get ’em back.

“If there’s anyone that can, it’s him and I was ready for that if it happened.

“If I get broken there we carry on.”

Such poise and patience perhaps come from the time Opelka spent off the court.

He has not been around much in recent years.

The former world number 17 had spent almost all of 2023, and a fair chunk of 2022 and 2024 on hiatus from tennis after hip and wrist surgeries.

He returned mid-way through the 2024 season, and is currently ranked 293rd in the world, with a protected ranking of 33.

“Yeah it was tough,” Opekla said on court.

“A lot of uncertainty, a lot of doubt.

“I watched Novak become the greatest in that two-year period off.

“A lot of guys, you find yourself, asking yourself, what would Novak be doing in my situation? Even when you’re in a sleeve, you’re always trying to maximise.

“And that’s kind of the effect he’s had on the sport.

“That’s how the sport evolves, competition.

“I stayed the course even when I was in the cast and on crutches and just hoping to have another chance out here like tonight.”

There will be no 100th ATP for Djokovic in the River City.

For this humble, softly spoken 27-year-old American though, suddenly everything has opened up, starting with another big server in Giovanni Mpetshi Perricard in Saturday night’s semifinal.

But that’s not Opelka’s goal.

“The big show’s in a week,” Opelka said.

“Obviously, this is great. This is all prep for Melbourne and this is just a step along the way.

“This is great, yeah, I’m excited, but it’s kind of the beginning of a new start for me.

“I gotta a long way to go to get my ranking back where I like it, and my endurance back where I like it to be, able to compete at this level week in, week out.

“You know, anyone can do it for a night or two here and there, but the difficult part is sustaining it over a year, over an 11-month season.”

It might have been the match of his life tonight.

But Opelka has shown that he will be a force to be reckoned with at Melbourne Park for the Australian Open.