WATCH Sinner in the ATP Finals LIVE in Australia on beIN SPORTS | Subscribe here and take advantage of our 7-day FREE TRIAL

Ruud, who reached the championship match on his previous ATP Finals appearance in 2022, expertly capitalised on a lacklustre performance from the third-seed to seal an 86-minute victory inside Inalpi Arena.

“It’s only one match, but it’s definitely one of the best wins of the season for me,” Ruud said. “In terms of who I’m playing, his level, his ranking and all this stuff. I feel very happy of course. I think we will see Carlos play better tennis than he did today, but I took care of my chances.

“I have not been [full of] confidence in the past weeks or months, so it was a great win for me and hopefully I can build on it, and I would like to get some more wins while I am in Turin.”

Although Alcaraz appeared below his physical best during the match, Ruud looked transformed from the player who entered the match having registered just two wins since the US Open. 

The 25-year-old struck the ball cleanly off both wings and showed few signs of nerves in serving out for his first Lexus ATP Head2Head win in five attempts against Alcaraz.

The early signs were good for Ruud as he began his third ATP Finals campaign. The No. 7 reeled off five consecutive games from 1-1 en route to the first set, although he was given substantial assistance by 15 unforced errors from the out-of-sorts Alcaraz.

Even when the Spaniard did begin to find his range in the second set, his comeback bid was undermined by his own inconsistency. Despite forging a 5-2 lead, Alcaraz was unable to close out and Ruud roared back with another streak of five games to seal his 50th tour-level win of 2024. The Norwegian had converted all four break points he earned, according to Infosys ATP Stats.

“It can be a bit tricky,” said Ruud, when asked about playing when an opponent is not at 100 percent. “I knew he was dealing with a bit of a cold. I saw him sniffling in the back area and with a tissue for his nose, so that’s a sign that maybe physically he won’t be necessarily at 100 per cent. 

"Of course, that is sad, and not good for him, but at the same time it is part of the game.

“I knew it coming in. I tried to make him play rallies and do my best, but it’s not easy because when you kind of know that someone is not 100 per cent, maybe you get stressed yourself. You think, ‘This is a really big chance for me to maybe try to win’. So I just tried to stay in my world, the moment, and luckily I got a good start. 

"I got a break early and kept it, and in the second set I was able to turn it around with some good tennis at the end.”

Ruud will next seek to earn a second win on Thursday, when he will face either Alexander Zverev or Andrey Rublev in John Newcombe Group. Monday’s defeat is an early blow to Alcaraz’s hopes of reaching the semi-finals in Turin for the second consecutive year, but the Spaniard will hope to raise his game for his next match as he chases his fifth tour-level title of the season.