As a fifth grader, he represented Kawasaki Municipal Mukai Elementary School at the 32nd First Life National Elementary School Tennis Championship and managed to reach the semi-finals.
At the age of 12, he passed the selection test for the Masaaki Morita Tennis Fund and went to the United States to train at IMG Academy in Florida.
1986
He became the lowest-ranked Tokyo semifinalist since then-World No. 479 Kelly Jones in 1986.
As a result he moved up more than 80 positions to World No. 131 in the rankings on 23 October 2023.
Following a quarterfinal showing at the Sydney Challenger he reached the top 130 in the rankings and 13th in the 2023 Next Generation ATP Finals race.
He made his debut in the main draw at the 2024 Australian Open as a lucky loser but lost to Tomáš Macháč in straight sets.
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Mochizuki's record against players who have been ranked in the top 10, with those who are active in boldface.
Only ATP Tour main draw matches and Davis Cup matches are considered:
2003
Shintaro Mochizuki (Japanese: 望月 慎太郎, Mochizuki Shintaro, born 2 June 2003) is a Japanese professional tennis player.
He has an ATP career-high singles ranking of world No. 129 achieved on 6 November 2023.
Shintaro Mochizuki was born on June 2, 2003, in Kawasaki, Kanagawa, Japan.
His name "Shintaro" was given by his father, inspired by the novelist and politician Shintaro Ishihara.
He started playing tennis at the age of 3.
2019
Mochizuki has a career-high ITF junior combined ranking of No. 1 achieved on 15 July 2019.
He began attending N High School in 2019.
Mochizuki won the 2019 Wimbledon Championships – Boys' singles title after becoming the first Japanese male to reach a Grand Slam juniors singles final.
In September that year, he led the Japanese team to win the Junior Davis Cup in Orlando, Florida.
In February, Mochizuki made his ATP main draw debut as a wildcard at the 2021 Singapore Tennis Open where he lost to Altug Celikbilek in straight sets.
In March, he qualified for his first ATP Masters 1000 main draw at the 2021 Miami Open having been given a wildcard for the qualifying competition.
He won his first-ever trophy as a professional by winning the Open Città della Disfida Challenger in Barletta, Italy, defeating the Argentine Santiago Rodriguez Taverna in straight sets.
He reached the top 200 at world No. 198 on 12 June 2023.
In July, he made his Grand Slam debut after qualifying for the main draw of the 2023 Wimbledon Championships but lost in the first round to 16th seed Tommy Paul in straight sets.
At the 2023 Hall of Fame Open he lost to Liam Broady also in the first round.
Ranked No. 215, he received a wildcard for the ATP 500 Japan Open.
After nine attempts, he finally won his first match at the ATP Tour level, beating Tomás Martín Etcheverry in straight sets.
Next he defeated top seed Taylor Fritz for his first top-10 win, to reach his first ATP tour-level quarterfinal.
In the quarterfinals, he defeated Alexei Popyrin to reach his first-ever semifinal.
