Morgan Pressel, intensifying her practice routines as she moves beyond her teens, shot a 7-under 65 on Friday to take a one-stroke lead over Suzann Pettersen midway through the Wegmans LPGA.
"You always have to be working ... harder because otherwise you are going to be passed pretty quickly out here," Pressel, the youngest major winner in LPGA Tour history, said after a second bogey-free round broke open a leaderboard logjam and got her to 10-under 134.
Defending champion Lorena Ochoa shot 70 to drop into a tie for 17th at 2 under. Annika Sorenstam (72), who is stepping away from the tour at the end of the season, finished her second round at 1 over and narrowly avoided being cut out of weekend play for the first time in 40 events dating to May 2006.
Pettersen, a five-time tour winner last year, chipped in for birdie on No. 9 _ her last hole _ to match Pressel's 65 and get to 9 under.
"I'm making a few adjustments right now to give myself ... a bit more consistency," the Norwegian star said. "I've been working hard on my game and not trying to get too hard on myself."
Inbee Park, who tied for fourth at the U.S. Women's Open in her rookie year in 2007, finished with a bogey to drop into third place at 8 under alongside Japan's Ai Miyazato (68). Both had been lodged in a seven-way tie for the lead after Thursday's opening round.
Christina Kim (67) and Cristie Kerr (70) were two shots back at 6 under.
"I've worked very hard on my game to get to this point," said Kerr, preparing for her title defense in the U.S. Women's Open next week. "It's nice that it's starting to peak a little bit ... going into the U.S. Open."
Michelle Wie, who is ranked 200th in the world and got in the tournament on a sponsor's exemption, matched her opening-round 71 to get to 2 under.
Vicky Hurst missed the cut with rounds of 77 and 71 after winning the Michelob Ultra Duramed Futures Players Championship on Sunday for her second Futures Tour victory of the year. She turned 18 on Thursday.
Pressel, who turned 20 four weeks ago, had to battle early on to tame the tricky, tree-lined Locust Hill course, sinking 10-foot and 18-foot putts on Nos. 3 and 4 to save par. She ran up five of her six birdies on the back nine, her laserlike irons setting up an array of chances inside 10 feet.
"I started hitting good shots and then was just missing the putts," she said. "I finally got a few to go in."
Since her breakthrough at the Kraft Nabisco Championship at age 18 in April 2007, Pressel has nine top-10 finishes. Her form dipped this spring _ she missed four cuts _ as she struggled to add distance off the tee and improve her short game. But she tied for second at the Sybase Classic in May and tied for sixth two weeks ago at the LPGA Championship.
"I worked pretty hard on my golf swing and I'm trying to make a couple of really big changes," she said. "I probably didn't work quite as hard on my short game ... so that probably is what set me back for a few events.
"If you are not practicing those kinds of (chip) shots, you are going to lose it quickly and I learned that."
Kim said she benefited from watching the "methodical way" in which Tiger Woods won the U.S. Open last weekend despite his knee injury.
"I've been so impatient in years past where you are hitting it to 5 feet every time, and you miss one, then you hit your tee shot in the trees on the next hole," said Kim, who has five top-10s this year. "It just mounts up, so I'm kind of tired with that."
The $2 million tournament, sandwiched between two majors, drew 88 of the top 100 money winners. Ochoa, who won in Rochester in 2005 and 2007, is seeking her seventh win of the season.