Not yet, at least.
Lewis, ranked No. 2 and a two-time winner this year, hopes to continue building her resume while closing in on Tseng this weekend in the NW Arkansas Championship at Pinnacle Country Club. The course is a familiar one for Lewis, who played at the University of Arkansas – about 20 minutes to the south – and unofficially won the rain-shortened event as an amateur in 2007.
Lewis won the Kraft Nabisco Championship last year for her first major title and finished second behind Tseng in the player-of-the-year race.
The Texan hasn't taken a back seat to anyone over her last five events this season – a stretch that's seen Lewis finish in the top five in each, including the two victories.
It's a stretch that has Lewis thinking this week about Tseng, the two-time defending champion of the NW Arkansas Championship, as the LPGA Tour prepares for next week's U.S. Open.
''I'm ready to take her on,'' Lewis said. ''I want to be No. 1 in the world. I know I'm two, but I'm not happy with that.''
Lewis' surge has come while Tseng has struggled over her last few events. Of course, Tseng's struggles are relative given that the she has been No. 1 for the past 70 weeks.
Tseng won three of her first five events this season, but she's finished outside the top 10 in each of her last two tournaments. That includes a 59th-place finish at the LPGA Championship earlier this month, during which the Taiwanese star opened with a 4-over 76 and failed to match or break par in any round while finishing 13 over.
''I put too much pressure on myself,'' Tseng said. ''I'm too hard on myself, but because everyone expects you to win every week. It's really hard to win every week, so now I want to smile more on the golf course, enjoy more on (the) golf course. I know if I'm enjoying the course then people are going to enjoy watching me.''
Tseng still leads the LPGA in earnings this season, with more than $1 million earned, but Lewis is closing in with more than $900,000. Tseng is well aware of Lewis' ability, as well as the favorable reception the hometown favorite and former Razorbacks standout will receive this weekend.
''You can always hear woo pig sooie,'' Tseng said. ''I'm like, 'Oh, she's making a birdie there.'''
Last year, Tseng won her second straight NW Arkansas Championship with a 4-foot birdie putt on the first hole of a playoff with Amy Yang. Two years ago, she overtook Michelle Wie with a final-round 65, including four birdies during a five-hole stretch on the back nine.
All in all, Tseng's past success has her feeling confident entering this weekend.
''I'm ready for the tournament, and I have so many good memories here,'' Tseng said. ''So I know I can play well here, and I just can't wait to build some confidence back with my game and just forget about the past and focus on every tournament.''
Lewis finished eighth at Pinnacle last year, her highest finish in the tournament since her unofficial win as an amateur. She said her recent success has her ready for even more this week, as well as in the future in her pursuit of Tseng.
''This is definitely a tournament that's up there with; it's a major for me,'' Lewis said. ''It's a tournament that I want to win.''