Germany's Alexander Zverev, the only two-time champion in the Nitto ATP Finals field, opened his play in the event with a 6-4, 6-4 victory over Russia's Andrey Rublev on Monday in Turin, Italy.

Zverev, the event's second seed, and Rublev, the eighth seed, began round-robin play in the John Newcombe Group.

In the other match on Monday, also in the Newcombe Group, sixth-seeded Casper Ruud of Norway upset third-seeded Carlos Alcaraz of Spain 6-1, 7-5.

The eight players in the season-ending tournament are split into two groups for the initial phase. The top two players from each group will advance to the semifinals.

Zverev, 27, captured the year-ending event in 2018 and 2021. He enjoyed a strong 2024 season, reaching three Grand Slam semifinals for the first time in his career. He lost to Alcaraz in the French Open final and advanced to the semifinals of the Australian Open.

On Monday, Zverev finished with a 9-3 edge in aces and a 22-10 advantage in winners. He never faced a break point and won on all seven of his net approaches.

"I thought it was a very solid match from my end," Zverev said. "Against anyone here, you have to play your best to have a chance, you have to be solid (and) mentally strong. I feel like I did that today, I felt like I used my chances quite well and I'm obviously happy with this win."

He isn't bothered by not being favorite this season and this week.

"I think the attention went to Carlos and Jannik (Sinner) all year long," Zverev said. "They deserve it, they won two Grand Slams each.

"It's normal in sports, at some point everybody retires, new players come along. We have a great group of guys leading with Jannik and Carlos. I think they had a better year, even though I'm No. 2 in the world. The benchmark is those two guys."

Alcaraz stumbled against Ruud, particularly at the key moments. Ruud saved five of the six break points on his serve while taking advantage of all four of his break opportunities.

"It's only one match, but it's definitely one of the best wins of the season for me," Ruud said. "In terms of who I'm playing, his level, his ranking and all this stuff. I feel very happy, of course. I think we will see Carlos play better tennis than he did today, but I took care of my chances."

The Ilie Nastase Group continues play Tuesday, with top-seeded Jannik Sinner of Italy opposing fifth-seeded Taylor Fritz of the United States while fourth-seeded Daniil Medvedev of Russia opposes seventh-seeded Alex de Minaur of Australia. On Sunday in round-robin action, Sinner defeated de Minaur 6-3, 6-4, and Fritz upended Medvedev 6-4, 6-3.

--Field Level Media