2026: 13th career title
In 2026, Tsitsipas participated in the United Cup to open his season in Perth. He won a straight sets match against Shintaro Mochizuki of Japan and a three-set grueling battle against Billy Harris of Great Britain. He then achieved his first top 20 win at any level since the Olympic Games in 2024, defeating Taylor Fritz in the quarterfinals. Team Greece would go on to lose the tie to Team USA and exit the tournament. Tsitsipas made a brief appearance in Adelaide the following week, losing to Aleksandar Vukic in straight sets. At the Australian Open, Tsitsipas improved on his previous year's result, losing in the second round to Tomáš Macháč.
Back in Athens, Tsitsipas played with Team Greece against Team Mexico, winning both of his matches in the Davis Cup World Group I play-offs. In Rotterdam, he lost to Botic van de Zandschulp in straight sets. In Doha, Tsitsipas won straight set matches against Moez Echargui and Daniil Medvedev, the latter being his first win against the Russian in four years, moving to his first tour-level quarterfinal in 10 months. He would lose the quarterfinal to Andrey Rublev in straight sets. In Dubai, Tsitsipas lost in the first round to Ugo Humbert, dropping out of the top 40 after failing to defend his title points.
During the Sunshine Double, Tsitsipas clashed with Denis Shapovalov in Indian Wells, losing in straight sets. With this loss, he briefly exited the top 50 but recovered after notching a second top 10 win of the season in Miami against Alex de Minaur in straight sets. He would move on to lose to Arthur Fils in his quickest defeat, only winning a singular game in the 55-minute straight sets encounter.
Beginning the spring clay season, he played in the Ultimate Tennis Showdown event held at the Arènes de Nîmes, losing to Andrey Rublev in the quartefinals, before winning against Ugo Humbert in the classification match. At the Monte-Carlo Masters, Tsitsipas recorded his worst run at the event, exiting in the opening round to Francisco Cerúndolo in straight sets and dropping out of the top 50 as a result. Failing to defend quarterfinal points from the previous year in Barcelona following an opening round loss to Fábián Marozsán in Munich, Tsitsipas dropped out of the top 80. He rebounded in Madrid, scoring three consecutive wins, including against world No. 11 Alexander Bublik. In the round of 16, despite holding two match points on serve in the deciding set, Tsitsipas lost to the defending champion, Casper Ruud. Facing Macháč again in Rome, Tsitsipas failed to score a win against the Czech in their first round encounter. In Geneva and Paris, Tsitsipas was unable to move past the second round in either tournament, losing to Learner Tien and Matteo Arnaldi.
On the grass, Tsitsipas re-entered the tour at the Mallorca Championships, a week before Wimbledon. He fell in the first round to Ignacio Buse in straight sets, notably complaining about the quality of the tennis balls in the process. On June 28, 2026, a day before the opening day at Wimbledon, Tsitsipas removed his father, Apostolos, from his coaching team, citing a desire to do 'something different'. He went on to exit the tournament after a straight sets defeat against eventual semifinalist, Novak Djokovic, in their first match since their final encounter at the 2023 Australian Open.
Following Wimbledon, Tsitsipas entered the summer clay court season in Gstaad, Switzerland. There, he won the tournament, winning four of his matches in deciding sets including one match completed over two days due to fading light. In the final, he defeated seventh seed Raphaël Collignon to claim his first title of the 2026 season and raising his ranking by thirty-one places to world No. 51.
At the 2026 US Open, Tsitsipas reached the fourth round, where he was defeated by eventual finalist Ben Shelton in straight sets. This was Tsitsipas's career-best performance at the US Open, eclipsing his 2020 and 2021 third round appearances, and it was his best grand slam performance since his quarter-final appearance at the 2024 French Open.