Defending champion Potter, 26, of Granger, Ind., came back from an early 1-down deficit and birdied the 17th hole to eliminate Charlotte Daughan, 2 and 1, in the morning’s Round of 32. She needed yet another comeback to eke out a 1-up Round-of-16 win over Lisa Schlesinger.

“We both had our moments out there where we really could have taken the match, but we just never really capitalized on it,” said Potter, a 2011 University of Missouri graduate who works for the Indiana Golf Office, of her victory over Schlesinger. “It’s just exhausting at this point. I’m just happy to make the quarterfinals.”

In her match with Schlesinger, Potter trailed on the inward nine for the first time in the championship. Schlesinger’s birdie at the par-4 10th gave her a 1-up lead, but Potter squared the match with a par 4 at No. 13.

The match turned at the par-5 17th. Both players drove into the right rough and while Potter was able to evade the low-hanging trees and reach the green in regulation, Schlesinger could not make a clean escape.

“Her shot was definitely the more difficult shot because she had more trees to work with,” said Potter, who won the hole with a two-putt par from 10 feet. “I just slightly pulled mine through the trees and it ended up working out well. Sometimes you’d rather be lucky than good, and that was one of those moments.”

Potter’s quarterfinal opponent will be 2010 U.S. Senior Women’s Amateur champion Mina Hardin, 54, of La Quinta, Calif. Hardin, who is also a two-time runner-up in USGA championships, eliminated Mariko Makabe in 19 holes in the Round of 32, and never trailed in her 5-and-4 Round-of-16 victory over Shannon Johnson.

Shirley, 28, of Atlanta, who lost to Potter in 19 holes in 2013, had a slightly easier route to victory. She cruised to a 5-and-4 win over 1987 Women’s Mid-Amateur runner-up Patricia Cornett in the morning round, but needed an afternoon comeback of her own to eliminate Tobi Herron, of Columbus, Ind., 2 and 1.

Just as she did in her Round-of-64 match on Monday, Shirley lost her lead with a three-hole string of bad play against Herron. After misclubbing on Nos. 7 and 8, she failed to get up and down from the rough on the par-4 ninth to hand Herron a 2-up lead.

“I hit it in the rough a few times today and you’re going to get in trouble for that,” said Shirley, a 2008 Auburn University alumna who works for Atlanta Junior Golf.

But Shirley’s luck quickly changed when Herron had her own streak of poor play. Three straight bogeys by Herron on holes 10-12 gave Shirley a 1-up lead, who reeled off eight consecutive pars en route to the victory.

“I keep having these little three-, four-hole bad stretches and luckily mine was on the front today and I was able to get it back on the back,” said Shirley. “You’re always going to have a match or two that you’re not going to hit it well, and that was this afternoon for me.”

Shirley’s quarterfinal opponent will be Debbie Adams, in a rematch of the 2013 Round of 16. Adams, 47, of Asheville, N.C., eliminated Kay Daniel and Lynne Cowan in the second and third rounds, respectively. Shirley beat Adams in 19 holes at Adams’ home course of Biltmore Forest Country Club in 2013.

Editor's Note: Cowan, a writer and contributor for AmateurGolf.com, had a nice run going that ended today but she didn't go down without a fight. Down three with three to play, Cowan won the 16th and 17th holes before running out of gas at the 18th. After qualifying as the ninth seed and winning two matches with her husband Carl on the bag, Cowan can return to California with head held high.

Christina Proteau, 31, of Canada, needed 19 holes to defeat both Alyssa Roland and Katie Miller. The challenging victories were extra sweet for Proteau, a prosecutor for British Columbia who is six months pregnant with her first child.

“I didn’t change my goals just because I was pregnant,” said Proteau, who also went to 19 holes in Monday’s Round of 64. “I wanted to win my first match, which is hard to do. It’s hard to get through Tuesday. Knowing that I am now exempt for next year is super exciting. I feel a little bit looser as each match goes on.”

Next up for Proteau is four-time Women’s Mid-Amateur champion Meghan Stasi, 36, of Oakland Park, Fla. Stasi, who eliminated Kimberly Noonan and Linda Jeffery on Tuesday, is attempting to become just the fifth person to win the same USGA championship at least five times.

Tara Joy-Connelly and Liisa Kelo Escartin round out the Women’s Mid-Amateur quarterfinalists. Neither Joy-Connelly, 41, of Palm Beach Gardens, Fla., nor Escartin, 28, of Mexico, trailed at any point on Tuesday.

All eight quarterfinalists are now fully exempt into the 2015 U.S. Women’s Mid-Amateur Championship, which will be held Oct. 3-8 at Squire Creek Country Club, in Choudrant, La.

The 2014 U.S. Women’s Mid-Amateur Championship consists of 36 holes of stroke play followed by six rounds of match play. The championship is scheduled to conclude with an 18-hole final starting at 9 a.m. EDT on Thursday.

The U.S. Women’s Mid-Amateur is one of 13 national championships conducted annually by the United States Golf Association, 10 of which are strictly for amateurs. It is open to female amateur golfers who are at least 25 years of age.