Carin Koch, Meg Mallon, Dawn Coe-Jones, Soo-Yun Kang and Sunny Lee finished two shots off the lead in a tie for second at 4-under-par 68.
Klein had a slow start at Berkleigh Country Club with one birdie and one bogey over her first nine holes, but the inward half was a different story.
She ran off back-to-back birdies starting at the par-4 10th and added a birdie at the 13th to move to 3 under.
Klein reached the green in two at the par-5 16th and took two putts for a birdie. At the par-4 17th, Klein hit a 9-iron to five feet for another birdie to keep the run going.
Klein found a greenside bunker with her approach at the par-5 last, but hit out to two feet and converted the short putt to make it three in a row.
'I just really hit that ball well today,' said Klein. 'Each week I've been getting better and better. Down the backside I hit it as good as I have all year.'
Klein, a three-time winner on the LPGA Tour, had a rough start to her season, including several missed cuts.
'I had some personal issues earlier this year, I'm going to leave it at that, which made the beginning of my year tough, but I've really been working on my game lately,' said Klein. 'Now I'm just ready to play golf.'
Koch, who gave birth to her second son earlier in the season, had five birdies and one bogey.
'I wanted to feel like I could play well when I came back out again,' said Koch. 'I've hit a lot of greens since I've come back, but I just haven't scored well. Today was a step in the right direction.'
Mallon played the back side first and picked up back-to-back birdies from the 15th to make the turn at 2 under.
She found trouble with a bogey at the seventh but recovered with a birdie at the eighth and rolled in an 18-footer for a birdie at the ninth.
'I gave myself a lot of opportunities for birdies and I didn't make any big mistakes,' said Mallon. 'After I made bogey I made two birdies, so that was good.'
Beth Daniel posted a 3-under 69 to join Laurie Rinker-Graham, Jamie Hullett, Kelly Robbins, Janice Moodie, Catriona Matthew and Pamela Kerrigan in a tie for seventh.
Defending champion Se Ri Pak, who won last week at the Jamie Farr, was one shot further back in a group at 2-under-par 70.
Suzy Whaley, who played the Greater Hartford Open on the PGA Tour last month, collected three birdies and three bogeys for an even-par round of 72.