The announcement that he would go up to play in the end-of-year men's round tournament for the first time in his life was received by Yannick Apron about five hours before the start of the game.
Matteo Bartini has announced his retirement following an injury, and Siner - the first replacement on the list - has been called up to take his place.
The Italian, who finished the year in ninth place, has in one moment become the youngest since Juan Martin del Potro in 2008 to take part in the prestigious tournament, which includes the top eight of the year.
He did so in front of the home crowd in Turin against the huge Pole Hubert Horacic, knowing that since 2011 it has not happened that a substitute player has won the tournament at the end of the year.
There was a lot of pressure on the shoulders of Apron, who only needed 1:20 hours to win 2: 6, 2: 6 and mention why everyone is sure he's the next big thing.
Here are just a few of the praises said about the 20-year-old Italian in recent years.
"He has all the tools to do something amazing in this sport," complimented American John Eisner and detailed: "He has a head on his shoulders, he is cold as ice, always maintaining stability and it is quite clear that he has not yet reached his peak."
Novak Djokovic added after a meeting between the two in Monte Carlo: "He has proven that he is not only the future of our industry, but also the present. He is a complete and talented player who can succeed on any surface."
"He's on a different level," Nick Kirius tweeted last month.
"I have never played against someone who beats like him," Alexander Zebrav concluded, "he has all the potential to be ranked first in the world. He is developing and improving at an incredible pace."
One thing that all these praises have in common is the agreement that an apron is a graph that is constantly rising, that there is still a lot of room for improvement, and that the good is still ahead of it.
Apparently this is due to the fact that until recently the Italian was not a tennis player at all.
Like anyone born in the northern part of Italy, in the region of the snow-capped Dolomites, Sinner practiced skiing as a child.
He was also excellent at it, and between the ages of 8 and 12 was considered one of the best in the country.
At the same time he played football and tennis occasionally, but only at the age of 13 made the decision to put the skis aside and concentrate exclusively on the bat and the green ball.
"Skiing felt to me like something dangerous and alienating," he explained, "tennis can be played all year round and in all weather conditions, and most importantly - you can see your opponent's face."
So apron packed a suitcase, moved to the academy of the esteemed coach Ricardo Fiati and kicked off his career.
Italian retired, Italian came in his place.
At least local fans are happy, Photo: EPA,
"I felt great on the field"
So far his progress is at the pace of a sprint.
The apron has almost no games for teenagers, because in 2018 he decided to jump into the water of the big ones.
Very quickly he won the Challengers, in 2019 he qualified for the first Grand Slam, stunned with a win in the "next generation" tournament and entered the first Maya in the world.
A year later he had already become the youngest since Djokovic to reach the quarter-finals at Roland Garros, and this year, after winning several tournaments, he was the first 2000s native to enter the top ten in the rankings.
"He can get where he wants if he continues like this," his coach Fiati recently declared.
Siner's unique career story has created a different beast in the landscape.
The variety of sports in which he practiced from an early age gave him strength and flexibility, alongside exceptional mental abilities that were reflected in the victory over Horkach.
"I felt great on the pitch and I hope to continue that," he said.
Tonight, against Daniel Medvedev (2), Sinner will try to achieve another victory and secure his place in the semi-finals, in what will be another meteor record.
The thing with him is that even if it does not happen now - it is clear to everyone that it will happen soon.
Yesterday:
Novak Djokovic secured his place in the semi-finals after beating Andrei Rublev 3: 6 2: 6.