TURIN, Italy — Carlos Alcaraz did not resemble the dominant force that secured two Grand Slam titles this year, suffering a 6-1, 7-5 defeat against Casper Ruud at the ATP Finals on Monday.

This marked Ruud’s initial victory over Alcaraz in their fifth encounter, a result that poses challenges for Alcaraz as he looks to progress from the round-robin stage at this prestigious event, featuring the top eight players of the year.

In 2023, Alcaraz celebrated wins at both the French Open and Wimbledon, bringing his Grand Slam total to four. However, he recently encountered difficulties at the Paris Masters, causing him to fall behind Alexander Zverev and land at No. 3 in the rankings this week.

Ruud, on the other hand, has shown strong performances in this season-ending tournament, having reached the semifinals in 2021 and the final in 2022 during his earlier appearances.

During the match, Alcaraz appeared poised to push the second set to a decisive game when he served at 5-4, only to be broken by Ruud unexpectedly.

Later in the same group, Zverev is scheduled to face Andrey Rublev. Only the top two players from each group will move on to the semifinals.

In another group, top-ranked Jannik Sinner and U.S. Open finalist Taylor Fritz claimed victories against Alex de Minaur and Daniil Medvedev, respectively, in matches held on Sunday.