Hannah Green's faltering third-round finish looks set to prove costly at the LPGA Tour's FM Championship in Boston.

The West Australian made five birdies for the day but a bogey on 15 and a double-bogey at the last saw her slip eight shots behind leader Miranda Wang after starting Saturday just three back.

China's Wang left the TPC Boston with a three-shot lead for a second straight day  after firing a seven under 65 to get to 18 under.

Wang took only 24 putts on the rain-softened course, and might have been helped by only have to play 18 holes. Some of her challengers faced much longer days because of storms that interrupted so much play the day before.

She holed an eight-foot birdie putt on the 18th hole to cap off a bogey-free round that gave her the three-stroke lead over Sei Young Kim (71) and Rose Zhang (67), with world No.1 Jeeno Thitikul (65) and Andrea Lee (66) a further shot back.

"This is where all the players want to be, so it's definitely special going into the final round being the sole leader," said Wang, who is seeking her first LPGA title. 

"This is what we try to do every week, so I'm just happy that I did my job really well. I hope to continue doing what I did today."

Green had to settle for a 70 and was tied 10th, two shots ahead of fellow Australian star Minjee Lee (70). Cassie Porter (69) was tied 37th at five under with Gabriela Ruffels (71) a further two stokes back.

Rookie Wang will try to extend a remarkable streak on the LPGA Tour this year. There have been 22 tournaments, all of them won by different players

She had eight birdies (along with a bogey) for a 29 on the front nine, an indication that she felt comfortable on the greens.

Zhang, who won her first LPGA event as a pro two years ago, has not had a top 10 against full field all year as she tried to split time between playing and finishing up at Stanford University.

"It's been a while since I've been in contention, so I'm very, very grateful," Zhang said.

She had to play 32 holes — 14 in the morning when she had a 64, and then she had four birdies in a five-hole stretch around the turn in the afternoon as she tried to keep pace with Wang.

"Feel like I'll I've been doing today is eating and drinking water and electrolytes," Zhang said. "It's been a while since I played 32 holes." 

-with AAP