Carlos Alcaraz’s bid for his first ATP Finals title took a major hit Monday as he fell 6-1, 7-5 to Norway's Casper Ruud in his opening match.
Despite the round-robin format offering a chance to recover, the third seed now faces a narrow path to progress, needing significant improvement in his remaining group matches.
Ruud, ranked seventh in the world, had previously lost all four encounters with Alcaraz, but he saved break points in the opening game and went on to dominate the first set as uncharacteristic errors crept into the Spaniard's game.
Alcaraz responded positively to move 5-2 ahead in the second set, breaking serve with a deft volley, and was two points from leveling the match, only to capitulate.
He dropped serve at 5-3 and looked forlorn as Norwegian Ruud roared to victory, winning the last five games.
Alcaraz, who won the French Open and Wimbledon titles this year, is hoping to become the first Spaniard to win the prestigious year-end title since Alex Corretja in 1998.
Ruud failed to convert his first two match points but closed it out on the third attempt to put himself in a strong position in the John Newcombe Group, which continues later Monday when Germany's Alexander Zverev takes on Russian Andrey Rublev.
"This is one of the best wins of the season for me," Ruud said in a courtside interview.
"I feel happy, of course. I've seen Carlos play better tennis than he played today, but I still had to take my chances."
The Ilie Nastase Group began Sunday with world No. 1 Jannik Sinner beating debutant Alex De Minaur and American Taylor Fritz overcoming Russian Daniil Medvedev.
While Alcaraz claimed the Beijing title in September, his form since winning Wimbledon has been patchy, including a second-round exit at the U.S. Open.
The 21-year-old made 34 unforced errors against Ruud, with his usually destructive forehand misfiring. Most of the drop shots he attempted either found the net or were easily dispatched by the grateful Norwegian.
Ruud, who reached the final in 2022 but lost to Novak Djokovic, said Alcaraz had been suffering from a cold in Turin.
"I knew he was maybe dealing with a cold. I’ve seen him snuffling around in the player area with tissues, so that’s a sign he may not be 100% physically," Ruud said.
"That’s sad for him, but it’s also part of the game, and I knew it coming in. I wanted to make him play rallies. I was able to turn around the second set with some good tennis at the end."