Sun played for the Atlanta Beat of the Women's United Soccer Association from 2001 to 2002. She was the first overall pick of the WUSA's Inaugural Draft, but a knee and ankle injury limited her first season with the Beat to 13 games with five starts. During the league's semifinal match against the Philadelphia Charge, the Beat were down 2–0, however, Sun scored on a penalty kick and then provided the assist on the equalizer goal with a corner kick headed in by Cindy Parlow. The Beat would go on to win the match 3–2. She then notched the Beat's third goal in the Founders Cup helping the team to an eventual 3–3 tie during regulation. The San Jose CyberRays won the title in a penalty kick shootout.