PORTLAND, September 1, 2013 (AFP) - The 24-year-old from Taiwan owns 15 LPGA titles and spent 109 weeks at number one -- a run that ended in March -- but she hasn't made it to the winner's circle in 36 events, since a triumph in the Kia Classic in March 2012.
Now out of the world top 10 at 15th in the rankings, she missed the cut in four of her last five tournaments.
However, she looked like her old, dominant self on Saturday at Columbia Edgewater Country Club with a round that included 11 birdies and two bogeys.
Her 54-hole total of 198 broke the tournament record of 199 set by Swedish great Annika Sorenstam in 2002, when the event was played over three rounds.
"It was awesome," Tseng beamed after coming from five adrift to take the lead. "It's great to be back in this position. I haven't been here for a long time."
Thailand's Pornanong Phatlum, who led after each of the first two rounds, carded a 71 and shared second on 201 with Norwegian Suzann Pettersen, who posted a 70.
World number two Stacy Lewis fired a 65 to move into a tie for fourth at 14-under, where she was joined by fellow Americans Morgan Pressel (65) and Lizette Salas (68) and Sweden's Anna Nordqvist (63).
Tseng caught fire early, with birdies at six of her first eight holes. She made the first of her two bogeys at the ninth, but bounced back with a birdie on 10.
Another bogey at the par-five 12th was followed by a birdie at the par-three 13th, which she said was key to her round.
"That's an important putt for me, and I think kind of a little turning point on the back nine," Tseng said of her 12-footer at 13.
She added three more birdies, at 15, 16 and 17 to gain breathing room on the field.
"I've been working really hard," Tseng said. "I want to get back in this position, so I don't feel any surprise because this is what I'm working hard for."
Pettersen, ranked number three in the world, was looking forward to playing with Tseng in the final group on Sunday.
"There's no one that I'd rather see playing better and playing well again than Ya-ni," Pettersen said. "I know she's been through a very rough patch.
"Like I said to her, she's just got to stay patient. She's too good not to kind of hang tough and be in the game."
Leading third-round scores on Saturday in the LPGA Safeway Classic (USA unless noted, par-72)
198 - Tseng Yani (TPE) 67-68-63
201 - Suzann Pettersen (NOR) 68-63-70, Pornanong Phatlum (THA) 64-66-71
202 - Anna Nordqvist (SWE) 69-70-63, Morgan Pressel 69-68-65, Stacy Lewis 67-70-65, Lizette Salas 66-68-68
203 - Karrie Webb (AUS) 69-67-67, Sandra Changkija 68-66-69, Cristie Kerr 66-68-69, Caroline Masson (GER) 69-64-70
204 - Austin Ernst 67-75-62, Maria Hjorth (SWE) 70-70-64, Brittany Lang 68-68-68
205 - Angela Stanford 71-67-67, Sandra Gal (GER) 66-66-73
206 - Beatriz Recari 71-66-69, Choi Na-Yeon (KOR) 70-66-70, Natalie Gulbis 68-68-70, Lexi Thompson 65-70-71
207 - Jodi Ewart Shadoff (ENG) 69-70-68, Jane Park 68-70-69, Lee Il-Hee (KOR) 67-71-69, Sydnee Michaels 67-70-70, Kwak Min-Seo (KOR) 69-67-71, Shin Ji-Yai (KOR) 68-68-71, Heather Bowie Young 67-69-71