ROCHESTER, N.Y. — After a breakout season on the LPGA Tour, Suzann Pettersen is tinkering with her swing again and keeping a tight lid on expectations.

"I'm a little bit surprised I'm playing this well, I must be honest," the Norwegian star said after shooting a 5-under 67 in the Wegmans LPGA today to open a three-stroke lead over Morgan Pressel and South Koreans Eun-Hee Ji and Inbee Park.

The 28-year-old Pettersen, a five-time tour winner in 2007, hasn't found her winning groove so far this year but has finishes of second, third and ninth in 10 events and is ninth on the money list. Her bogey-free round got her to 14-under 202.

"It's not like I'm surprised I'm playing solid, but I have less expectations, so maybe that's good," she said. "Of course you want to win tournaments, but a tournament is a four-day race and you've got to make sure you're there every day. There's no room for mistakes. At least I'm in a good position for tomorrow."

Ji, who has ties for fourth and ninth in her second year on tour, holed out from 170 yards to open with an eagle and ran up six more birdies for a 64 and a second-place tie at 11 under.

"I had some lucky holes today," said the 22-year-old Seoul native, whose best finish was second to Pettersen at South Korea's Kolon Championship in October. "I wouldn't say it's my turn to beat her. ... It's more about winning my first LPGA tournament."

The 19-year-old Park (69), who tied for fourth at the U.S. Women's Open in her rookie year in 2007, shot her third sub-70 round. And Pressel (71), who held a one-stroke lead over Pettersen after the second round, got her only birdie on the last hole.

"Nobody is unbeatable out there," Pressel said. "I'm not going to say I can't catch her (Pettersen), but she played great today."

Japan's Ai Miyazato and South Korean Hee-Won Han were at 9 under.

Han, a six-time tour winner between 2003 and 2006, matched Ji's 64 — the day's best round — with six birdies in seven holes after the turn. She played a limited schedule in 2007 after the birth of her son, Dale, and recently traveled home to celebrate his birthday, which falls on Sunday.

A thunderstorm on an otherwise sunny, 79-degree afternoon halted play for almost two hours at the Locust Hill course, a traditional, 72-par layout with narrow, tree-lined fairways and compact greens.

Cristie Kerr, preparing for her title defense in the upcoming U.S. Women's Open, was tied for seventh with Jeong Jang at 7 under. Kerr had a double bogey on No. 6.

In her fifth year on tour, Pettersen finally got her breakthrough at the Michelob Ultra Open in May 2007 and picked up her first major at the LPGA Championship a month later — shredding the never-won tag of a top talent. In October, she won three of four events she played.

Birdies on Nos. 3 and 4 put her ahead of Pressel, and Pettersen picked up another birdie after chipping to 6 feet on No. 11. She two-putted for birdie on No. 17 and finished with a 15-foot birdie putt on the last green.

The $2 million tournament, sandwiched between two majors, drew 88 of the top 100 money winners.

Top-ranked Lorena Ochoa (68) birdied three of the first four holes, lost some momentum on the back nine but finished with an eagle and a birdie to reach 6 under. The 26-year-old Mexican won in Rochester in 2005 and 2007 and is seeking her seventh win of the season.

With $1.9 million in season earnings, Ochoa has a half-million-dollar lead on Annika Sorenstam. The Swede, who is stepping away from the tour at the end of the season, shot a second straight 72 to stay mired at 1 over.

Michelle Wie was 1 under after a 73.