Wimbledon champion Carlos Alcaraz suffered a shock opening defeat to Casper Ruud at the season-ending ATP Finals in Turin on Monday.
Norwegian star Ruud blew the John Newcombe Group wide open with a stunning 6-1 7-5 victory over world No 3 Alcaraz at the Inalpi Arena.
Ruud, who reached the championship match on his previous appearance in 2022, capitalised on a lacklustre performance from the Spaniard to close out the match in 86 minutes.
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"It's only one match but it's one of the best wins of the season in terms of who I am playing and his ranking," said Ruud during his on-court interview.
"I feel really happy, of course. I think we have seen Carlos play better tennis but I took care of my chances.
"I haven't been boosting with confidence in the last few months so it's a great win for me, and I would like to get some more wins in Turin. I knew he was dealing with a bit of a cold perhaps.
"I've seen him snuffling around in the area here and always with a tissue for his nose, so physically he might not be at 100 per cent. It's sad and not good for him, but it's part of the game.
"I tried to make him play rallies and do my best. I got a good start, I got a break early and in the second set I managed to turn it around with some good tennis at the end."
Ruud, who had lost all four of his previous meetings against Alcaraz, saved break points in the opening game but dominated the first set from then on as surprising errors flowed from the Spaniard's racket.
Alcaraz failed to hold serve in the opening six games, while he was unable to capitalise on five break points as he surrendered the first set in 36 minutes.
However, the 21-year-old initially appeared to have restored order during a strong start to set two as he moved 5-2 ahead, breaking serve with a deft volley, and was two points from levelling the match - only to capitulate.
He dropped serve at 5-3 and looked forlorn as Norwegian star Ruud went on to win five games in a row to seal an impressive victory, with Alcaraz swiftly departing the court.
Alcaraz, who won the French Open and Wimbledon titles this year, is hoping to become the first Spaniard to win the prestigious year-ending title since Alex Corretja in 1998.
Ruud later told Sky Sports' Tim Henman: "I play as an underdog. In the past I've been able to do well here."
He will next seek to earn a second win on Wednesday, when he will face Andrey Rublev after he lost 6-4 6-4 to Alexander Zverev.
After the defeat, Alcaraz said: "A few days before coming here I got sick at home. The days that I was practising here, it was feeling OK. Not pretty good, but OK.
"I could play, I could feel that I can get into the rallies, in the practice. Obviously in the matches it's totally different."
'Alcaraz's drop shots were a bail out'
"We certainly do owe him an apology. I think I said Alcaraz in straight sets," said Laura Robson, a former British No 1, told Sky Sports Tennis.
"We weren't expecting that at all. I was looking at the numbers after the match and he managed to win only 50 per cent of his first serves.
"Ruud was just steady and didn't over-play.
"Seeing that around in the practice court gives him some hope and confidence. Alcaraz was wearing strips over his nose because he was struggling with breathing.
"He started with some conviction and there wasn't much going on for Carlos, it was surprising to me.
"It's difficult when you're trying to play a drop shot in these conditions, its perhaps not the best shot selection. For me, it was a bit of a bail out."
Tale of the Tape
Ruud's record vs top-10 opponents
Zverev begins quest for third ATP Finals in style
Zverev ignited his pursuit for a third year-end trophy with a commanding victory against Rublev on Monday evening.
Zverev, fresh from replacing Alcaraz as world No 2, triumphed in just 72 minutes and sent down nine aces a week on from his Paris Masters win.
It earned Zverev a Tour-leading 67th win of the season and ensured he made the perfect start to his pursuit of a third ATP Finals victory after success at the 2018 and 2021 editions.
Speaking to Laura Robson, Zverev said: "I'm looking forward to the next few matches and hopefully I can improve on a few more things, because I don't think this match was perfect to be honest. I still think there's a few more things that can be better.
"I missed a few balls from the baseline and I feel I wasn't as sharp movement-wise as I would like to be. You always have to find ways to improve."
Tale of the tape
How the John Newcombe Group looks...
Sinner collects year-end No 1 trophy
The Italian said: "It's a very exclusive club being the No 1 in the world and it's the ultimate goal we have. Fifty-two weeks of consistent tennis and it wouldn't be possible without the people around me.
"Continue to keep people close to you who you are comfortable with. These are the people who are always going to help you."
What makes Sinner so special?
"You look at his tennis skills. His serve has got better but for me it's his ball-striking from the back of the court," said Henman.
"He's got long levers and although he doesn't look the strongest physically, in terms of shot for shot I don't think anyone hits the ball harder.
"His movement in and out of the court and his defensive skills have improved, and I think he's looking to finish a few more balls at the net. He's doing all the right things."
Tuesday at the Nitto ATP Finals on Sky Sports Tennis
- Former champion Daniil Medvedev takes on Alex de Minaur at 1pm (GMT) in the Ilie Nastase Group.
- World No 1 Jannik Sinner faces American Taylor Fritz from 7.30pm.
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