Carlos Alcaraz looked little like the player who won two Grand Slams this year in a 6-1, 7-5 loss to Casper Ruud at the ATP Finals on Monday.

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 year’s top eight players.

Alcaraz won the French Open and Wimbledon this year to boost his career total to four Grand Slam titles. But he also struggled at the Paris Masters recently and dropped behind Alexander Zverev to No. 3 in the rankings this week.

Ruud reached the semifinals and final in his first two appearances at the season-ending tournament in 2021 and 2022, respectively.

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

Later in Alcaraz’s and Ruud’s group, Zverev plays Andrey Rublev.

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

Top-ranked Jannik Sinner and U.S. Open finalist Taylor Fritz beat Alex de Minaur and Daniil Medvedev, respectively, in the other group on Sunday.