Early career Mmoh enjoyed early success on the
ITF Futures tour, winning three titles before turning 18.
2016–17: ATP, Grand Slam and top 200 debut In February 2016, Mmoh qualified for his first ATP-level tournament at
Memphis by defeating fellow Americans
Dennis Novikov and
Bjorn Fratangelo. He then lost in the first round to eventual finalist
Taylor Fritz, the highest ranked American teenager at the time. Following his fourth Futures title, Mmoh was awarded a wildcard into the
Miami Masters, where he lost to
Alexander Zverev, the top-ranked 18 year-old in the world, after dropping two tiebreaks. In September 2016, Mmoh broke into the top 300 for the first time by reaching the final of the
ATP Challenger event at
Tiburon as a qualifier. In November 2016, he reached the Top 200 and also won the
2017 Australian Open Wild Card Challenge largely by winning his first career
Challenger title at
Knoxville. He would claim another Challenger title the following summer in August 2017 at
Lexington.
2018: Top 100, First ATP wins & quarterfinals, Masters third round To start off the 2018 season, Mmoh recorded his first career ATP-level match wins by defeating
Federico Delbonis in the first round of the
Brisbane International and world No. 33
Mischa Zverev to make the quarterfinals, where he lost to
Alex de Minaur. At the
2018 Miami Open he reached the third round as a qualifier for the first time at a Masters level defeating 12th seed
Roberto Bautista Agut for his first top-15 win and the biggest of his career. He entered the main draw at the
2018 Wimbledon Championships for the first time at this Grand Slam as a lucky loser. He reached the top 100 at World No. 97 on 1 October 2018.
2019–20: First Grand Slam win In January 2019, Mmoh qualified for the first time via ranking in a Grand Slam main draw at the
2019 Australian Open where he lost in the first round to
Radu Albot. At the
2020 Australian Open, Mmoh recorded his first main draw victory with a straight sets win over
Pablo Andújar as a wildcard. Following his Australian Open performance, Mmoh qualified for the main draw at the
2020 US Open, where he won his first round match against
João Sousa in four sets, and also at the
2020 French Open, where he lost in the first round.
2021–22: ATP quarterfinal, Out of top 250 At the
2021 Australian Open he reached again the second round in a five set stunning comeback against
Viktor Troicki but lost to second seed
Rafael Nadal in the next round. He received a wildcard for the
2021 Miami Open. In 2022, he entered the
2022 U.S. Men's Clay Court Championships as a lucky loser directly into the second round replacing top seed
Casper Ruud who withdrew in the last minute. He won his first match defeating
Sam Querrey to reach the quarterfinals but withdrew due to injury. Mmoh won a wildcard entry into the main draw at the
2022 French Open by winning the Roland Garros wildcard challenge.
2023–24: Best season: Two Major third rounds, ATP quarterfinal, top 85, hiatus Mmoh's first tournament of the year was in
Pune, where he defeated local wildcard
Manas Dhamne in the first round before losing to the 6th seed,
Filip Krajinović in the second round. He then entered the
2023 Australian Open as a lucky loser after the withdrawal of
David Goffin and won his first round match, defeating fellow qualifier French
Laurent Lokoli, after saving a match point in the third set. He then defeated 12th seed
Alexander Zverev in the second round. He became the fifth player to make it as a lucky loser to the third round; the furthest a lucky loser had made it at this Major is the fourth round (
Stéphane Robert in 2014). As a result he moved up 25 positions back into the top 100 to a new career-high singles ranking of No. 83 on 30 January 2023. In February, he lost in the first round at the
Dallas Open to eventual champion
Yibing Wu. The following week, he reached the round of 16 at the
Delray Beach Open by defeating wildcard
Aleksandar Kovacevic in three sets. He then reached the quarterfinals after upsetting third seed
Denis Shapovalov, also in three sets. As a result, he reached a new career high ranking of No. 82 on 20 February 2023. In early March, Mmoh suffered a leg injury at the
Mexican Open during his second round match against
Tommy Paul and did not return to competition until May at the
French Open, where he lost in the first round to ninth seed
Taylor Fritz. He entered the
2023 Wimbledon Championships as a lucky loser again and defeated 11th seed
Félix Auger-Aliassime in the first round. In July 2023, in
Washington, D.C., he defeated world No. 17
Hubert Hurkacz, and in
Winston-Salem he beat
Marcos Giron as a wildcard. Next he defeated 11th seed
Karen Khachanov in the first and
John Isner in the second round of the
US Open. It was Isner's last singles match before retiring from professional tennis.
2025: Out of top 400, comeback to the ATP Tour He fell out of the top 400 on 3 February 2025. Mmoh qualified for the main draw of the
Delray Beach Open defeating
Radu Albot and
Dmitry Popko. He then beat
Alexander Shevchenko to reach the second round, where he retired against
Alex Michelsen after winning the first set. ==Singles performance timeline==