Three strokes behind playing partner Lewis overnight in the opening women’s major of the season, the in-form Tseng fired a superb six-under-par 66 to end a blustery afternoon two ahead of the chasing pack.

The long-hitting Taiwanese recorded six birdies in a flawless display at Mission Hills Country Club on a sun-baked course playing fast and firm for a 12-under total of 204.

Tseng, who claimed last year’s title by one shot over Norway’s Suzann Pettersen, will go into Sunday’s final round as a heavy favorite to land her fourth major victory.

She has already triumphed four times across the globe this year and her power game is ideally suited to the 6,738-yard Dinah Shore Tournament Course at Mission Hills.

“I feel very excited,” the ever-smiling Tseng, 22, told reporters. “It’s always good to have six birdies and no bogeys out there on this tough golf course. I had fun out there.

“I played pretty aggressive. I wanted to catch Stacy, so I really hung in there and played really good today.”

Tseng, who drew level with Lewis after seven holes before edging ahead for the first time at par-five 11th, relished the opportunity to add another major trophy to her cabinet.

“I’m not afraid that I’m leading right now,” she said after being followed by more than 50 members of Oak Valley Golf Club in nearby Beaumont where Tseng used to play.

“I’m not afraid that I have a two-shot lead. I just want to enjoy it and I know how to play one shot at a time.”

Lewis, who duelled for the lead with Tseng for most of the day, slipped back with a three-putt bogey at the 16th to finish alone in second after carding a 71.

Although the 26-year-old birdied the ninth and 13th to stay level with Tseng, she ultimately paid the penalty for poor driving which forced her to scramble on several holes.

“It was a really hard round,” said Lewis. “I’m exhausted as I hit it in the rough all day and was just struggling to make pars. I’m really glad for the day to be over.

“But she’s playing great right now, and it’s hard because she’s got a pretty good chance of making birdie almost every hole. It definitely puts pressure on me. I just have to go play some good golf tomorrow, too.”

On a high-quality leaderboard, 2007 champion Morgan Pressel was alone in third at eight under after a 69, two strokes better than fellow American Michelle Wie, who also shot a 69.

Wie, who produced three top-10s in her first four appearances at Mission Hills as a teenager, reeled off four birdies in six holes on the back nine but missed a two-foot putt.

“I didn’t mis-hit it,” the 21-year-old Hawaiian said. “It just broke a lot for a two-footer, a lot more than I thought.

“Obviously I still have a long way to go, and I really want it (victory), so hopefully tomorrow I’ll have a lot of birdies.”

Sunday’s final round is firmly in Tseng’s control, however, and the talkative Taiwanese sounded an ominous warning to her rivals by saying she is playing the best golf of her life.

“I started very good this year, and every tournament I keep building the confidence,” she said.

“Even if I have a bad shot, I still try to build the confidence for myself. I just want to keep doing my job.”