The recent winner of the Kraft Nabisco Championship, Park on Monday moved to the top spot in the Rolex Rankings for the first time in her career. She leads Lewis by .04 points as the LPGA returns to action this week with the Lotte Championship in Hawaii.
'This is a very big day in my golf career,' Park said.
'It's nice to reach this goal, but I know a lot of players are close to No. 1. It gives me something else to play for every week and I know it's going to be a lot of fun.'
The Rolex Rankings are based on a two-year rolling points table, with an emphasis on the most recent 52 weeks and weighed even more heavily on the past 13 weeks.
Park won twice last year and posted a scoring average of 70.21 to receive her first Vare Trophy.
This season, the 24-year-old has already won twice, including the Kraft Nabisco Championship, and earned more than $567,000.