Tseng won the ANZ RACV Ladies Masters Sunday in Australia a week after taking the Women's Australian Open. She opened her year with a victory at the Taifong Ladies Open in her native Taiwan.
She began 2011 ranked No. 5 but the early success boosted her to No. 1 for the first time. Tseng is the sixth player to top the world women's golf rankings.
She has a ranking average of 10.34 points, just ahead of Jiyai Shin (10.18), who had been No. 1 for the previous 15 weeks. Suzann Pettersen (9.47) moved to third and pushed Cristie Kerr (9.44) to fourth.
The only other change in the Top 10 found Paula Creamer (6.31) edging past Michelle Wie (6.29) into 10th with Wie at No. 11.
Choi Na-yeon (9.40) is fifth and Ai Miyazato (8.91) comes in at sixth. Kim In-kyung (7.38) is in the seventh spot ahead of No. 8 Ahn Sun-ju (6.75) and ninth-ranked Kim Song-hee (6.39).
The LPGA Tour officially opens its 2011 schedule this week with the Honda LPGA in Thailand.