Ochoa, who has won seven times in the last 12 months, moved 0.14 average points in front of Sorenstam even though the LPGA Tour was off over the weekend.
The Mexican star has five top-10 finishes in just six starts this season, including a win at the Safeway International and a runner-up at the last LPGA event, the Ginn Open.
Her climb to No. 1 was set in motion last year, when she won six times on the way to being named the LPGA Tour's Player of the Year. It was precipitated recently by a serious back injury to Sorenstam, which will keep the Swede sidelined for at least a month.
Sorenstam assumed the No. 1 spot when the rankings debuted last year, and has had a stranglehold on it ever since.
Well, until recently.
'I have been dreaming of getting to that position for many, many years,' Ochoa said recently. 'I have been getting closer and closer with each year. Finally this year, it could happen. I am right there, close and playing good. I am going to keep it going and get to the top.'
Already at the top, she could extend her lead over Sorenstam this week with another good finish at the Corona Championship in her native Mexico.
In fact, a good finish may be inevitable: At last year's Corona, Ochoa ran off three straight rounds in the 60s (including a course-record 64 on Saturday) to cruise to a five-shot win.
'For me, it's like a U.S. Open, being able to play in my country and win in front of my people,' she had said.
Elsewhere in the top 20, little changed.
Karrie Webb remained No. 3, where she was followed again by Morgan Pressel, Cristie Kerr and Paula Creamer. Ai Miyazato moved up one spot to No. 7, bumping Juli Inkster to No. 8, while Jeong Jang, Shiho Ohyama, Se-Ri Pak and Brittany Lincicome remained in positions 9-12.
Stacy Prammanasudh slipped into the No. 13 spot, dropping Pat Hurst to 14th, and Hee-Won Han, Mi Hyun Kim, Jee Young Lee, Julieta Granada, Yuri Fudoh and Michelle Wie rounded out the top 20 in the same positions they held last week.