In 2009, Tseng became the fastest player in LPGA history to reach the $2 million mark in career earnings, achieving it in 32 events over 1 year, 1 month, and 13 days, piping Paula Creamer's record in 2006 by three whole months.

In 2010, Tseng had an extremely successful year, winning four tournaments, three of which were on the LPGA. She won the Kraft Nabisco Championship, her second-career major victory, by one shot over Suzann Pettersen. She also managed to win the HANDA Australian Women's Open on the Ladies European Tour (LET), the RICOH Women's British Open (her second major victory of 2010) and the P&G NW Arkansas Championship Presented by Walmart.

In 2011, Tseng started the season in impressive fashion winning the ISPS Handa Women's Australian Open by 7 strokes. A week later Tseng shot a closing 68 to win the ANZ RACV Ladies Masters at the Royal Pines resort and claimed the world No. 1 ranking from Korean Jiyai Shin.

She became the youngest player to win consecutive Rolex Player of the Year awards, clinching the honour with five events remaining on the 2011 schedule; also won her first Vare Trophy for lowest scoring average with a final scoring average of 69.66. She won seven LPGA events, including two majors, and topped the LPGA Official Money List with $2,921,713; also won four international events.  At 22 years, 6 months, 8 days, Tseng became the youngest player ever, male or female, to win 5 majors after claiming the Ricoh Women's British Open.

World number 1 Tseng carried on her remarkable form with 8 top 5 finishes in 2012 including three victories at The Honda LPGA Thailand, RR Donnelley LPGA Founders Cup and The Kia Classic. She also became the quickest female golfer in LPGA history to pass the $8 million mark in career earnings.