With the medical incident in the crowd and Alcaraz's treatment, that was a disrupted first set, so let's hope for a clearer run through the second.

Sinner saving that set point lifted the Italian and his already noisy support. They can sense an incoming home win, so what does Alcaraz have left in the tank?

Alex de Minaur suffered at Sinner's hands on Saturday, losing to the Italian who now holds a 13-0 record against the Australian.

Afterwards, De Minaur offered insight into how Sinner can be so clinical compared to most other players in the sport.

"I do think there's more constant pressure. That's the biggest thing with Jannik," De Minaur said.

"More often than not I feel like with Jannik you can get into a bit of a snowball effect. After one break, the second break comes, and all of a sudden you're doing your best to fight off potentially a bagel or 6-1.

"That's mainly due to how well he's returning and his serving at the moment. His level is insanely high. You're going to have to bring a very high level to beat him."

Jannik Sinner takes the first set! He hasn't dropped a set at the ATP Finals in Turin since the 2023 title match!

Carlos Alcaraz was stood well behind the baseline to receive a second serve. The pair get into a lengthy groundstroke exchange, with Alcaraz creeping forward with every shot.

However, Jannik Sinner executes another excellent lob to bring up set point.

Jannik Sinner is relentless! He chases down a drop shot, lobs Carlos Alcaraz and is poised at the net to hammer home the smash!

Alcaraz wins the next one but Sinner is two points away from taking the first set.

Another backhand error from Carlos Alcaraz, this time firing long.

However, Jannik Sinner gives away his advantage, attempting a forehand drop shot but putting it into the tramlines. That wasn't the time for experimentation.

A golden opportunity for Jannik Sinner goes begging! Carlos Alcaraz poorly executes his drop shot and Sinner gets there with time to spare. However, his cross-court backhand clips the top of the net.

No matter! Alcaraz sends a backhand wide!

Those groans are replaced by cheers as a big second serve down the T sends Carlos Alcaraz scrambling.

The crowd groans as Jannik Sinner sends a shot wide.

A forehand winner with both feet off the ground followed by a wide serve which ricochets off Carlos Alcaraz's racquet and into the net.

Jannik Sinner has saved another break point in Turin - I make that his 13th.

Tie-break time!

Jannik Sinner fires down a huge second serve to save set point!

We have a break point! And it's also set point for Carlos Alcaraz, who comes out on top of a net battle.

Carlos Alcaraz's forehand, which was a bit iffy in the opening couple of games, is back to its best at the business end of the first set. I think I need a keyboard shortcut for forehand winner down the line...

A whipped cross-court forehand from the Spaniard takes the 12th game to 30-all.

Jannik Sinner shuts down any suggestion of a break point with a well-placed ace but Alcaraz earns deuce with a delicate drop shot.

Carlos Alcaraz gets down low for a forehand volley from outside the service box?! He gets a little stranded as he comes into the net but Jannik Sinner can't execute a tricky lob.

He holds to 15 with a forehand down the line and Sinner once again finds himself serving to stay in the opening set.

Three big first serves. Three brisk points. 40-0 to Jannik Sinner.

The Italian loses his radar a little, including sending down a double fault for 40-30, but recovers with an ace.

Carlos Alcaraz jogs back into position. Jannik Sinner is serving to stay in the set.

While Carlos Alcaraz receives treatment, Jannik Sinner does a few keepy uppies with a tennis ball.

Jannik Sinner sprays a forehand winner to get the crowd on their feet. Carlos Alcaraz says anything you can do, I can do better, sending down a booming forehand of his own to hold to 30.

At the change of ends, the physio comes out to have a look at Alcaraz's right thigh. The Spaniard is taking a medical timeout.

He was stretching his leg at the end of Sinner's previous service game.

That's more like the Jannik Sinner we've seen this week! He finds a couple of big first serves, including a fourth ace of the evening, to race to 40-0.

He blots his copybook with a simple forehand into the net but serves and volleys off a wide serve to close out the hold.

Anyone else sensing a lot of tie-breaks to come?

Laura Robson
Former British number one on Sky Sports

What I loved most about that Sinner backhand line winner was straight afterward you saw the reaction from Alcaraz, but a minute after that when he was at his towel box he gave Sinner's camp a little nod of approval.

So it was a smile shared between the two of them.