Lulu Sun

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.

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.

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 and the fourth with a win over Zhu Lin. She equalled the feat of reaching the fourth round at the All England Club as the first New Zealand female player in the Open Era, and second after Dame Ruia Morrison in 1957 and 1959. She reached her first quarterfinal with a win over Emma Raducanu becoming the first New Zealand woman to ever reach that stage at Wimbledon in the Open Era. She was only the second woman from New Zealand to reach a major quarterfinal, following Belinda Cordwell at the 1989 Australian Open. Her run finally ended in the quarterfinals where she was beaten in three sets by Donna Vekić. She would go on to represent New Zealand at the 2024 Olympics in singles, where she entered as an alternate, as well as in doubles.

Ranked No. 64, she qualified for the Cincinnati Open making her debut at this WTA 1000, and defeated Linda Nosková in the first round, 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.