Alexander Zverev won his second Nitto ATP Finals title on Sunday.

Mischa Zverev and Alexander Zverev lift the Nitto ATP Finals trophy on Sunday.

Alexander Zverev and Daniil Medvedev embrace at the net on Sunday.

Alexander Zverev hammers a forehand against Daniil Medvedev on Sunday.

Alexander Zverev celebrates his second Nitto ATP Finals title.

Alexander Zverev celebrates winning the Nitto ATP Finals title with his dogs.

Trophy ceremony at the Pala Alpitour.

Pierre-Hugues Herbert celebrates winning the title in Turin with his baby.

Alexander Zverev celebrates his second Nitto ATP Finals title.

Pierre-Hugues Herbert/Nicolas Mahut capture their second Nitto ATP Finals title.

Alexander Zverev claims the first Brad Drewett Trophy handed out in Turin.

Pierre-Hugues Herbert celebrates his Nitto ATP Finals title with his family on Sunday.

Alexander Zverev celebrates his second Nitto ATP Finals title.

The families and team members of Nicolas Mahut and Pierre-Hugues Herbert celebrate their Nitto ATP Finals title success.

Nicolas Mahut and Pierre-Hugues Herbert celebrate lifting the Nitto ATP finals trophy on Sunday in Turin.

Pierre-Hugues Herbert and Nicolas Mahut keep Rajeev Ram and Joe Salisbury under pressure on Sunday at the Nitto ATP finals.

Rajeev Ram and Joe Salisbury fight hard on Sunday against Pierre-Hugues and Nicolas Mahut in the title-match of the Nitto ATP Finals.

Pierre-Hugues Herbert and Nicolas Mahut win 20 of their 25 service points in the first set of the title-match Sunday at the Nitto ATP Finals.

Alexander Zverev defeats Novak Djokovic on Saturday in Turin.

Casper Ruud falls to Daniil Medvedev on Saturday in Turin.

Daniil Medvedev defeats Casper Ruud on Saturday to reach the final in Turin.

Rajeev Ram (net) and Joe Salisbury beat Nikola Mektic and Mate Pavic on Saturday to reach the Nitto ATP Finals title match.

Novak Djokovic will face Alexander Zverev in the semi-finals on Saturday at the Nitto ATP Finals.

Novak Djokovic defeats Cameron Norrie on Friday in Turin.

Casper Ruud defeats Andrey Rublev to reach the semi-finals in Turin on Friday.

Andrey Rublev and Jerome Kym pose after a training session at the Nitto ATP Finals.

Rajeev Ram and Joe Salisbury will play Nikola Mektic and Mate Pavic on Saturday in the semi-finals of the Nitto ATP Finals.

Horia Tecau and Kevin Krawietz celebrate Tecau's final ATP Tour win on Thursday.

Horia Tecau signs autographs on Thursday after his final ATP Tour match.

Daniil Medvedev moves through with a 3-0 record in the Red Group.

Jannik Sinner plays with great composure to recover from a slow start on Thursday against Daniil Medvedev at the Nitto ATP Finals.

Daniil Medvedev defeats Jannik Sinner on Thursday in Turin.

Julian Knowle, Martin Klizan, Viktor Troicki, ATP Chairman Andrea Gaudenzi, Paolo Lorenzi and Steve Darcis pose at the Pala Alpitour in Turin.

Hubert Hurkacz won three tour-level titles in 2021.

Alexander Zverev defeats Hubert Hurkacz on Thursday in Turin.

Horia Tecau and Kevin Krawietz end their partnership with victory on Thursday at the Nitto ATP Finals in Turin.

Andrea Gaudenzi presents Jannik Sinner with an award for cracking the Top 10 of the FedEx ATP Rankings.

Cameron Norrie falls to Casper Ruud in three sets on Wednesday in Turin.

Casper Ruud claims his first win of the Nitto ATP Finals over alternate Cameron Norrie.

Novak Djokovic records his 50th match win of the season on Wednesday to qualify for the semi-finals at the Nitto ATP Finals.

Juan Sebastian Cabal and Robert Farah beat Jamie Murray and Bruno Soares on Wednesday at the Nitto ATP Finals.

Juan Sebastian Cabal and Robert Farah were ruthless against Jamie Murray and Bruno Soares on Wednesday at the Nitto ATP Finals.

Jannik Sinner makes his Nitto ATP Finals debut with a 6-2, 6-2 win against Hubert Hurkacz.

Daniil Medvedev is 2-0 in Red Group action at the Nitto ATP Finals.

Jannik Sinner defeats Hubert Hurkacz on Tuesday in Turin.

Alexander Zverev hits a forehand against Daniil Medvedev on Tuesday in Turin.

Daniil Medvedev defeats Alexander Zverev on Tuesday in Turin.

Horacio Zeballos and Marcel Granollers barely put a foot wrong on Tuesday in the first set against Nikola Mektic and Mate Pavic at the Nitto ATP Finals.

Stefanos Tsitsipas is making his third appearance at the Nitto ATP Finals.

Cameron Norrie is the second alternate at this year's Nitto ATP Finals.

Novak Djokovic lifts the 2021 year-end ATP Tour No. 1 trophy presented by FedEx on Monday in Turin.

Novak Djokovic defeats Casper Ruud on Monday in Turin.

Rajeev Ram and Joe Salisbury got off to a fast start against Jamie Murray and Bruno Soares on Monday at the Nitto ATP Finals.

Alexander fires a serve against Matteo Berrettini on Sunday in Turin.

Italian suffers an injury during his opening match in Turin on Sunday.

Matteo Berrettini and Alexander Zverev embrace after Berrettini retires from their Nitto ATP Finals match.

Hubert Hurkacz fires a backhand against Daniil Medvedev on Sunday in Turin.

Daniil Medvedev moves to 1-0 in Red Group action on Sunday in Turin.

Alexander Zverev is pursuing his second Nitto ATP Finals title.

Daniil Medvedev, who beat Hubert Hurkacz on Sunday at the Nitto ATP Finals, has won 23 of his past 26 matches.

Daniil Medvedev hit 15 aces to beat Hubert Hurkacz on Sunday at the Nitto ATP Finals in Turin.

Mate Pavic and Nikola Mektic receive the year-end No. 1 doubles trophy at the Nitto ATP Finals on Sunday.

Mate Pavic and Nikola Mektic celebrate beating Kevin Krawietz and Horia Tecau on Sunday at the Nitto ATP Finals.

Mate Pavic and Nikola Mektic were presented with the year-end No. 1 doubles trophy on Sunday at the Nitto ATP Finals.

Top seeds Nikola Mektic and Mate Pavic beat Kevin Krawietz and Horia Tecau in the Green Group on Sunday at the Nitto ATP Finals.

Daniil Medvedev is pursuing his second consecutive Nitto ATP Finals title this week.

Hubert Hurkacz is making his Nitto ATP Finals debut.

Casper Ruud will face Novak Djokovic on Monday in his first group match at the Nitto ATP Finals.

Matteo Berrettini will begin his 2021 Nitto ATP Finals on Sunday evening against Matteo Berrettini.

Andrey Rublev, Alexander Zverev, Matteo Berrettini, Novak Djokovic, Daniil Medvedev, Stefanos Tsitsipas, Casper Ruud and Hubert Hurkacz walk towards the Piazza San Carlo in Turin

Matteo Berrettini will try to thrill his home fans in Turin during his second appearance at the Nitto ATP Finals.

Alexander Zverev won the 2018 Nitto ATP Finals title, when the season finale was held at The O2 in London.

Nikola Mektic and Mate Pavic reach the semi-finals of the Nitto ATP Finals for the first time as a team.

Casper Ruud celebrates beating Andrey Rublev on Friday to qualify for the semi-finals at the Nitto ATP Finals.

Pierre-Hugues Herbert (front) and Nicolas Mahut reach the final of the Nitto ATP Finals in Turin for the third time.

Nikola Mektic and Mate Pavic look to cap their banner debut season with the Nitto ATP Finals title.

Daniil Medvedev is looking to become the first back-to-back champion since Novak Djokovic in 2015.

Jannik Sinner still has a shot of reaching the semi-finals in Turin.

Andrey Rublev falls to Novak Djokovic in their first career meeting at the Nitto ATP Finals in Turin.

Joe Salisbury and Rajeev Ram save two match points to go 2-0 at the 2021 Nitto ATP Finals in Turin.

Casper Ruud recovered from a set down to beat Cameron Norrie at the Nitto ATP Finals.

Pierre-Hugues Herbert and Nicolas Mahut made a triumphant return to the Nitto ATP Finals.

Casper Ruud led Novak Djokovic by a break but lost in straight sets on his Nitto ATP Finals debut.

Andrey Rublev avenged his 2020 Nitto ATP Finals defeat to Stefanos Tsitsipas at the 2021 tournament in Turin.

Ivan Dodig and Filip Polasek kept their semi-final hopes alive at the Nitto ATP Finals on Tuesday.