Carlos Alcaraz loses ATP Finals opener against Casper Ruud

Carlos Alcaraz struggled with a stomach issue and looked far from the player who won two grand slams this year in losing to Casper Ruud 6-1, 7-5 at the ATP Finals on Monday, local time.

It marked Ruud's first victory over Alcaraz in five career meetings, and the result could make it difficult for Alcaraz to advance from the round-robin stage at the season-ending event for the top eight players.

"I didn't feel well on court," Alcaraz said.

"A few days before coming here, I got sick at home … This morning, I feel uncomfortable in the stomach."

Alcaraz won the French Open and Wimbledon to boost his career total to four grand slams titles. But he also struggled at the Paris Masters recently and dropped behind Alexander Zverev to number three in the rankings this week.

"I have no experience playing on indoor courts," Alcaraz said.

"I'll be a really good player on indoor courts, I'm sure about it. But I think it's about time, about getting experience … A lot of players are better than me on indoor court."

Casper Ruud had never beaten Carlos ALcaraz in five previous meetings. (Getty Images: sportinfoto/DeFodi Images)

Ruud reached the 2021 semifinals and 2022 final in his first two appearances at the finals. But he has struggled recently, too, losing his first or second match in his last seven events.

"I'm not full of confidence," Ruud said. "A match like today might be able to change it."

Alcaraz was broken when he served for the second set at 5-4.

Alcaraz led 25-16 in winners but committed 26 unforced errors to Ruud's 10.

Ruud converted all four of his break points while Alcaraz was just one of six in that category.

"I'm tired mentally," Alcaraz said.

"Obviously a lot of matches, really tight schedule, really demanding year with not too many days off."

Later in Alcaraz's and Ruud's group, Zverev beat Andrey Rublev 6-4, 6-4.

Zverev, who won the finals in 2018 in London and 2021 in Turin, extended his winning streak to six matches following a title run at the Paris Masters.

Rublev is making his fifth consecutive appearance at the finals but hasn't won a match at the event since 2022.

The top two finishers from each group advance to the semifinals.

AP