Choi had a 73 to match the second-ranked Tseng at 7-under 137 on the BosqueReal Country Club course. Ochoa, the first-round leader after a 65, shot a 73 to drop into a tie for third with Pat Hurst (70) with one round left.
The steep and scrubby BosqueReal course has always been tough for Ochoa. She has yet to win this tournament in four attempts. Last year, she opened with a 4-over 76 ' her worst score in nearly a year ' and ended up tying for eighth.
Choi said she didnt feel pressured challenging Ochoa on her home turf.
I just want to play and enjoy and just keep doing it, Choi said.
Tseng had seven birdies, a bogey and a double bogey.
I had a bet with Lorena for bogey-free, and Im like, Oh, my God, I made a bogey on the first hole, Tseng said. I had seven birdies today, and I had one four-putt, and thats really bad.
Ochoa said gusty wind made play difficult, but was confident she would come back Sunday.
The important thing is that Im still in there, she said.
The tournament is Ochoas third of the season. She won the Honda LPGA Thailand for her 25th tour title, then tied for sixth in Singapore.
The Mexican star always draws the biggest crowds when shes at home. Her biggest fans are young, ribboned pre-teens who want to follow in her footsteps.
One of them was Ana Porias, a 10-year-old golf enthusiast who opted to spend her birthday weekend chasing down player autographs and whispering about putting strategy on the 18th green.
Her father, Stephan Porias, said Ana decided to take up golf a year ago after being inspired by Ochoa. Saturday was the pairs fifth LPGA tournament starring Ochoa in Mexico.
We share a lot playing golf together, he said, then turned to his daughter. Now if we could only get your mother and brothers to play!
Despite her fame in Mexico, Ochoa wasnt the only player getting attention Saturday. When Natalie Gulbis walked onto the 18th green in a short skirt and white sweater, the crowd broke out into catcalls and whistles.
Ochoa will be back in Mexico for two other tournaments this year. The Corona Championship is next month in Morelia and the Lorena Ochoa Invitational is in November in Guadalajara, Ochoas hometown.