Juniors As a teenager, Sun entered a number of
ITF Women's Circuit events, playing as Lulu Radovcic and later changed her last name to Sun, her mother's maiden name. Sun represented Switzerland as a junior, finishing runner-up with
Violet Apisah in the
2018 Australian Open girls' doubles. She also played under the New Zealand flag at junior Wimbledon that year, losing in the second round in
singles and the first round in
doubles.
2021–2022: NCAA champion, professional debut Before turning professional, Sun played one season of college tennis for the
Texas Longhorns in 2020–21. She went 15–1 on singles court three and 6–1 on court two. In the final of the
2021 NCAA tournament, Sun won the championship-clinching match for the Longhorns to beat
Pepperdine 4–3. Sun partnered Kylie Collins in the team's top doubles spot, going 22–4 in dual matches, and they reached the final of the NCAA doubles tournament but fell to
North Carolina's
Makenna Jones and
Elizabeth Scotty. In May 2022, she won her first big ITF title at the
Saint-Gaudens Open, partnering
Fernanda Contreras in doubles. She made her
WTA Tour main-draw debut at the
Morocco Open two days later, where she received a wildcard into the singles draw, but lost to seventh seed
Arantxa Rus in the first round.
2024: Wimbledon quarterfinal, WTA 500 final, top 40 Sun made her Grand Slam debut at the
Australian Open after qualifying but was beaten in the first round by
Elisabetta Cocciaretto. On her WTA 1000 debut, she recorded her first win at that level at the
Dubai Championships as a wildcard, following the retirement of
Paula Badosa. She lost to ninth seed
Jelena Ostapenko in the second round. In April, Sun played under the
New Zealand flag for the first time as part of the team for the 2024
Billie Jean King Cup. In May, Sun won the singles and doubles titles at the W100 Bonita Springs Championship in Florida. She reached the top 125 on 17 June 2024. She qualified for the
2024 Wimbledon Championships making her debut at this major and upset eighth seed
Zheng Qinwen in the first round. It was her first top 10 win, and also her first completed victory over any player in the top 100. Next, she reached the third round with a win over fellow qualifier
Yulia Starodubtseva before losing to 15th seed
Marta Kostyuk. Sun followed this result by reaching her first WTA Tour-level final at the newly upgraded WTA 500
Monterrey Open, with wins over
Chloé Paquet,
María Lourdes Carlé,
Erika Andreeva and third seed
Ekaterina Alexandrova. She lost the final to Linda Nosková in straight sets. As a result she reached world No. 41 on 26 August 2024 and the top 40 two weeks later. At the
US Open, Sun retired due to a hip injury after losing the opening set of her first round match against
Lucia Bronzetti. Having taken a month off tour, she returned to the court at the
China Open, but lost in the first round to
Ashlyn Krueger. Sun withdrew from her next scheduled tournament, the
Hong Kong Tennis Open, and announced she was bringing an end to her 2024 season. In December, Sun was named
WTA Newcomer of the Year.
2025: First WTA 125 title, Guangzhou final Having suffered opening round defeats in her first four tournaments of the 2025 season, Sun secured her first win of the year at the
Abu Dhabi Open, overcoming
Caroline Garcia. She lost to eighth seed
Leylah Fernandez in the second round. In March, at the WTA 1000 event in
Indian Wells, she defeated
Rebecca Šramková and 31st seed Linda Nosková to reach the third round, where her run was ended by eighth seed Zheng Qinwen. Partnering with
Leylah Fernandez, Sun was runner-up in the doubles at the
WTA 125 Catalonia Open in May, losing to
Bianca Andreescu and
Aldila Sutjiadi in the final. The following week at the
Italian Open, she defeated wildcard entrant
Giorgia Pedone to reach the second round, in which she lost to sixth seed
Jasmine Paolini. Sun lost in the first round at the
French Open and
Wimbledon to
Victoria Mboko and
Marie Bouzková respectively. Moving onto the North American hard-court swing of the season at the
Canadian Open, she defeated
Sorana Cîrstea in the first round, but lost her next match to fifth seed
Amanda Anisimova. A win over qualifier
Antonia Ružić saw Sun into the second round at the
Cincinnati Open, at which point she lost to 12th seed
Ekaterina Alexandrova. At the
US Open, she defeated
Camila Osorio to record her first win at a major since the 2024 Wimbledon Championships. Sun lost to 19th seed
Elise Mertens in the second round. In September, Sun won her first WTA 125 title at the
Jingshan Open, defeating
Ma Yexin in the final. Having made it through qualifying at the
Guangzhou Open in October, she defeated top seed
Jéssica Bouzas Maneiro, wildcard entrant
Wang Yafan,
Caty McNally and qualifier
Claire Liu to reach her second WTA Tour final. Sun lost the championship match to second seed
Ann LI in straight sets. Despite the loss, she returned to the world's top-100, moving up 28 places to No. 88 on 27 October 2025. ==Performance timelines==