However Ochoa held her nerve to add another stroke to her overnight lead and heads the field on 16 under par, with American Paula Creamer and Swede Annika Sorenstam joint second on eight under.
Australia's Karrie Webb is a shot further back, while America's Laura Diaz is on five under.
On a day of blustery winds and sporadic rain, Ochoa was one of just four players who shot under 70 at the Tanah Merah Country Club, and is also the only player to shoot sub-70 scores for the first three rounds of the event.
"I'm just happy that the day is over and that I'm still in the lead," said Ochoa.
"I'm just happy that the day is over and that I'm still in the lead."
"It was a tough day, starting with the rain in the morning, and then I didn't feel as good a rhythm as I have the first two days."
The 26-year-old accepted she had to work hard to save par on several occasions.
"I got good up-and-downs and I was in the bunker a few times and then I put myself in good position on the greens," said Ochoa, who ended Sorenstam's streak of five consecutive Player of the Year awards in 2007.
"It was very different from the first two rounds but I still managed to score and that's what matters."
Chasers not giving up
Creamer admitted it would take a big turn of form from Ochoa in the fourth round to secure an improbable win, but she was not giving up hope.
"I know it's going to take a lot and I'm going to need a little help from Lorena, but anything is possible," said the Californian.
"Lorena knows we're not right behind her but we're within reach. I'm ready to go low and I'm sure Annika is too."
Sorenstam said she was trying to stay positive and that she had overcome a bigger deficit than the eight-shots she faces in Singapore.
"I came from 10 behind in one," the Swede recalled.
"There's no doubt that it's a tough test. Lorena is playing some great golf. But you just have to continue to believe in your own game.
"There's some birdies out there, I've proven that, and I just have to remember that tomorrow."