2021 ATP Finals – Singles
Alexander Zverev defeated the defending champion Daniil Medvedev in the final, 6–4, 6–4 to win the singles title at the 2021 ATP Finals. It was his second ATP Finals title, the first being in 2018. With the win, Zverev ended a six-year streak of different winners at the tournament, extending back to 2015. Novak Djokovic was attempting to tie Roger Federer's record of six ATP Finals titles, but lost in the semifinals to Zverev. Hubert Hurkacz, Casper Ruud, Jannik Sinner (as an alternate replacing Matteo Berrettini) and Cameron Norrie (as an alternate replacing Stefanos  Tsitsipas) made their debuts at the event. Sinner became the youngest player to win a match at the year-end championships since Lleyton Hewitt in 2000. He was the youngest to compete since Juan Martin del Potro in 2008 and the first alternate to win a match since Janko Tipsarević in 2011. Draw. Red group. † Following ATP rules, Berrettini's retirement against Zverev was counted as a straight-set loss in determining round robin standings.