The diminutive Japanese star shot a two-under 70 on Friday at TPC Boston for a share of the lead in the FM Championship with Hyo Joo Kim and US Solheim Cup qualifier Allisen Corpuz.
Kim and Corpuz each shot 67 to join the four-foot-11 Yamashita at nine-under 135.
Yamashita has four LPGA Tour titles, also winning the Meijer LPGA Classic in June in Michigan after taking the Women's British Open in Wales and Maybank Championship in Malaysia last season as rookie of the year. She has 13 Japan LPGA victories.
Kim also has two victories this season, the Founders Cup and Ford Championship.
"It's been a while since my name has been on the leaderboard," Kim said.
Morgane Metraux (65) and Ruoning Yin (65) and Jenny Bae (68) were a stroke behind the leaders. Nataliya Guseva (68) and Emily Kristine Pedersen (72) are at seven under.
First-round leader Sei Young Kim followed her opening 64 with a 74 to fall three strokes back.
Top-ranked Nelly Korda had her second straight 72 to make the cut on the number in the final event before the Solheim Cup matches in the Netherlands.
Major winner Hannah Green (67) is tied 27th and Australia's leading contender.
The 2019 women's PGA champion is six behind the leaders and two ahead of compatriot Robyn Choi (70) and Karis Davidson (73).
European captain Anna Nordqvist advanced to the weekend in her final event on the LPGA Tour. The Swede rebounded from an opening 74 with a 68.
"I couldn't really sleep last night because it was so much emotions running through my head," she said. "It was really tough yesterday afternoon with those gusty winds."
Corpuz wrapped up the last automatic place on the U.S. team last week in Canada.
"I've been hitting the ball really well and putting myself in the right spots." Corpuz said.
The $4.4 million purse is the largest outside of the majors on the LPGA Tour.
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