In 2002, Sun continued her success at the next level, winning two $25k tournaments: firstly in April at Ho Chi Minh City, Vietnam, where she defeated Zheng Jie in the semifinal and Jeon Mi-ra in the final [source: [WTA Official Website](https://www.wtatennis.com/)], and then in August at Beijing, overcoming Zheng Jie again in the semifinal and Rika Fujiwara in the final [source: [WTA Official Website](https://www.wtatennis.com/)].

In 2003, she reached the final of a $50k tournament in Modena, entering as a lucky loser and defeating several high-quality opponents such as Martina Suchá, Maret Ani, and Gala León García before losing to Melinda Czink in the final [source: [Tennis Abstract](https://www.tennisabstract.com/)].

She qualified for Doha, defeating Yuliana Fedak, Ľubomíra Kurhajcová, and María Sánchez Lorenzo, but lost in three sets to Nicole Pratt in the opening round [source: [WTA Official Website](https://www.wtatennis.com/)].

Sun also competed in the 2004 Summer Olympics, where she won a gold medal in women's doubles with her partner Li Ting, defeating Conchita Martínez and Virginia Ruano Pascual of Spain in the final [source: [Olympics Official Website](https://olympics.com/)].

Her career-best win came at Beijing, where she defeated Serena Williams in the second round before losing to Maria Kirilenko [source: [WTA Official Website](https://www.wtatennis.com/)].

On 27 January 2008, Sun captured her first Grand Slam title in mixed doubles at the Australian Open, partnering with Nenad Zimonjić to defeat Sania Mirza and Mahesh Bhupathi in straight sets [source: [Australian Open Official Site](https://ausopen.com/)].