Norway's Casper Ruud eased to a straight-sets victory over an out-of-sorts Carlos Alcaraz on Monday as the Spanish star's bid for a maiden ATP Finals title got off to a poor start.

Ruud, 25, romped through the opening set before fighting back from 5-2 behind in the second to win 6-1, 7-5 in Turin.

World number three Alcaraz, who won the French Open and Wimbledon titles earlier this year, made 34 unforced errors in an uncharacteristically errant display.

"I'm tired. I'm tired mentally," said Alcaraz. "Obviously a lot of matches, really tight schedule, really demanding year with not too many days off, not too many periods for you could rest.

"Some players deal with it better than others," he went on to say.

It was Ruud's first victory over 21-year-old Alcaraz in their five career meetings.

"I had two good times in Turin before – this part of the season has not been good for me but hopefully I've saved some wins for this week and I've started well," said 2022 runner-up Ruud, who had suffered seven defeats in eight matches coming into this tournament.

Alcaraz struggled with sickness and adapting to the indoor surface.

"A few days before coming here, I got sick at home," said the Spaniard. "I don't like to sound like I'm making excuses, but today I didn't feel well on court.

"It doesn't matter the times I beat Casper," he added. " I have no experience playing on indoor courts – I have to be better on this part of the year that we play on indoor courts." (AFP)