'Not human': Tennis world in disbelief over Novak Djokovic moment

Novak Djokovic, pictured here in action against Andrey Rublev at the ATP Finals.
Novak Djokovic had the tennis world in awe at the ATP Finals. Image: Tennis TV/Getty

Novak Djokovic had the tennis world in awe on Wednesday as he raced into the semis at the ATP Finals in stunning fashion.

The World No.1 claimed a spot in the last four with a 6-3 6-2 victory over Russian Andrey Rublev.

Djokovic, who won his opener against Casper Ruud on Monday, looked to be in trouble in his first-ever match against Rublev when he was broken in the first game.

'SAD TO HEAR': Tennis world reacts to devastating Roger Federer news

'NO LOGIC': Nick Kyrgios cops backlash over Australian Open call

However he soon took complete control of Wednesday's round robin clash.

The Serb, looking for his sixth title at the season-ending event, was given an immediate reprieve when Rublev double faulted in his own service game to bring up two break points, the second of which went for Djokovic.

The pair were on an even keel until the eighth game, when Djokovic pounced on a heavy volley from Rublev and sent a winning pass beyond the Russian to claim the vital break on his way to the first set.

The second was more assured from the World No.1, forcing his opponent into some costly errors that helped bring up Djokovic's 40th win at the ATP Finals in 68 minutes, sealed with an ace.

One particular moment early in the second set had commentators and fans in awe.

Rublev appeared destined to win a rally at 1-1, 40-40, only to watch Djokovic show why he's one of the greatest defenders the sport has ever seen.

Djokovic went into a full split to retrieve one ball on his forehand side, before racing to the other side of the court to produce a lunging winner that left Rublev gobsmacked.

"Quite incredible stuff from the World No.1," one commentator said on Tennis TV.

"How is that for athletic ability, full stretch on the forehand side."

His co-commentator added: 'Djokovic just made this his house, showing what he is capable of.

"The very best defender of all time on a hard court."

Stefanos Tsitsipas forced to withdraw with injury

Djokovic tops the Green Group standings with two wins from two and is assured of his place in the last-four.

"I served well (and) that helped tremendously," Djokovic said.

"I wanted to put him out of his comfort zone, taking away the time and mix up the pace. It was a great performance overall.

"Winning the first set, I put additional pressure on him, and I started to maybe play more consistently from the back of the court."

Novak Djokovic, pictured here after beating Andrey Rublev at the ATP Finals.
Novak Djokovic celebrates after beating Andrey Rublev at the ATP Finals. (Photo by Giampiero Sposito/Getty Images)

Earlier, Greek World No.4 Stefanos Tsitsipas, who had been carrying a right elbow injury since the Paris Masters earlier this month, withdrew and was replaced by British World No.12 Cameron Norrie.

"I have taken the very difficult decision to retire from the 2021 Finals due to my elbow injury, which has been bothering me for a couple of weeks now," Tsitsipas said.

"It's a very difficult decision from my side."

Norrie made his debut in the tournament later on Wednesday against Norway's Ruud.

Norrie is the second alternate drafted in following Italian Matteo Berrettini's withdrawal on Tuesday, with compatriot Jannik Sinner taking his place.

Djokovic's win leaves Norrie with an outside chance of making the semis despite playing a match fewer than his rivals.

with AAP

Click here to sign up to our newsletter for all the latest and breaking stories from Australia and around the world.