India's teen tennis sensation Sania Mirza is notching up wins and confidence, booking into the third round of the Acura Classic with a straight-set upset of fourth seed Nadia Petrova.

Despite an off day for the defeated Russian, Mirza, whose ranking has risen to 59th after a breakaway season, is pleased with her progress from a qualifying start in this hardcourt event played at a golfing resort on the Californian coast.

"When you play the world number 8, nothing is easy," Mirza said after her 6-2, 6-1 win over Petrova on Wednesday. "Even a nil-nil score line would not have been easy.

"If I had relaxed for even one second, she would have jumped all over me. "I had a game plan, I knew what I wanted to do - I'm glad I could do it."

The comprehensive win moved the 18-year-old into a confrontation against Japan's Akiko Morigami on Thursday at the $1.3-million event.

Mirza has been on a tear this season, becoming the first Indian woman to lift a WTA title when she triumphed at home in February at Hyderabad.

Her debut at the tournament has so far gone well past plan after a pair of straight-set wins.

Mirza now stands 22-12 this season. Russia's Petrova, a one-time world number sixth now ranked ninth, has yet to win a career title.

"I wanted to attack one of her weaknesses," Mirza said of her upset result. "Maybe she didn't play as well as I've seen her before.

"She's a big girl with a big serve; she started with two aces, but the key today was to move her around."

Mirza said her second set went quicker than she might have expected. "I believed I could win even before the match. But the scoreline was easier than I expected," she said.

"But I know that anyone is beatable."

Mirza said that after her first career title at home in February, her tennis progress has gone faster than she would have dared to dream.

"A lot has happened from a season which I started as a qualifier in Tasmania. But I'm not complaining, I've worked hard. It's very satisfying to see yourself getting closer and closer to a title.

"I believe in short-term goals. That was to be in the Top 50, If I get there, anything that happens afterwards will be a bonus."