Tseng turned professional in January 2007. She competed on the Ladies Asian Golf Tour and won the DLF Women’s Indian Open. She also competed on the CN Canadian Women’s Tour, where she won the CN Canadian Women’s Tour at Vancouver Golf Club.
In September 2010, Tseng was offered a five-year sponsorship deal from a Chinese company worth $T1 billion (US$25 million) with access to a luxury villa and private jets. Tseng rejected the offer because one of the requirements of the deal was that she switch her citizenship to the People’s Republic of China.
In January 2011, Tseng defended her title at the Taifong Ladies Open on the LPGA of Taiwan Tour. Three weeks later she won the ISPS Handa Women’s Australian Open and a week later the ANZ RACV Ladies Masters, both events co-sponsored by the ALPG Tour and the Ladies European Tour. Her wins moved her into the number 1 position in the Women’s World Golf Rankings. She won again the next week in the first tournament of the LPGA season, the Honda LPGA Thailand.
In June 2011, she firstly won the LPGA State Farm Classic over Cristie Kerr by 3 strokes. Two week later, she subsequently won the LPGA Championship. This meant she was the youngest player to have achieved four LPGA majors. Tseng had initially moved five shots ahead the day before her win. She then tried to break a further record by making 20 under but failed with one stroke. Tseng described her achievement as “very special”.