Shirley, 28, of Atlanta, built a 3-up lead through nine holes, but she bogeyed Nos. 10-12 as Smith squared the match.

“I got a little agitated with myself – I’m not going to lie,” said Shirley, the 2013 Women’s Mid-Amateur runner-up. “But I just tried to walk a little slower and gather my thoughts, try to hit some good golf shots.”

Shirley regained the lead when Smith missed her par putt at the par-4 15th, and ultimately won the 18th with a two-putt par for the hard-earned win.

“I just had a bad stretch,” said Shirley, a manager of Rules and competitions for Atlanta Junior Golf. “That’s going to happen, especially on a golf course like this. You just have to make sure you don’t get too down on yourself.”

Next up for Shirley will be Patricia Cornett, 60, of Mill Valley, Calif., who rolled to a 6-and-4 win over Lea Venable. Cornett, a past USA Curtis Cup player and captain, was the runner-up to Cindy Scholefield in the inaugural U.S. Women’s Mid-Amateur in 1987.

In the day’s biggest upset, playoff survivor Connie Isler, 30, of Arlington, Va., eliminated No. 2 seed Dawn Woodard, 40, of Greer, S.C., by a 2-up margin. Isler built a 3-up lead through eight holes, and Woodard could not gain any traction, despite her marked length advantage off the tee.

“Just as I think I get a little momentum, she would make birdie or do a little something to kill that momentum,” said Woodard, who held the lead following Monday’s first round of stroke-play qualifying. “For a while, it seemed like everything went her way and nothing went mine.”

“It sounds very clichéd, but I just tried to stay in the moment,” said Isler, a former player and coach at Georgetown University who now works in sales for IBM. “Dawn hits it super far, so I just tried to play my own game. I always tried to play like I was down, even though I was never down.”

Woodard had a prime opportunity to square the match at the par-4 13th, but her birdie putt lipped out. Isler promptly stuck her approach to 3 feet on the par-4 15th and converted the birdie. While Woodard was able to win No. 16 to get back to a one-hole deficit, her tee shot at No. 18 flew far right and she could not get up and down.

“I did leave a lot of little shots just out to the right today,” said Woodard. “I wasn’t quite as crisp. But still I didn’t think I hit it bad enough to lose. Only a handful of people today would have beaten me. She just happened to be one of them.”

Woodard continued her match-play struggles at the Women’s Mid-Amateur. In her 13 championship appearances, she has reached the quarterfinals twice, but hasn’t advanced past the second round in the other 11 tries.

Julia Potter, 26, of Granger, Ind., continued her title defense with a 2-and-1 win over Audrey Akins, 47, of Canada. Potter never trailed in the match, but also was not able to gain more than a 1-up advantage until No. 17, which she won with a birdie.

“I didn’t hit a green until 6, but Audrey played great,” said Potter, who also earned medalist honors in 2013 en route to her 19-hole victory over Shirley in the final match. “She made some clutch putts at the beginning.”

Potter will next face Charlotte Daughan in Tuesday morning’s Round of 32. Daughan, 30, of Orlando, Fla., cruised to a 6-and-5 win over 2004 U.S. Women’s Mid-Amateur champion Corey Weworski.

Christina Proteau, 31, of Canada, was 2 down and dormie to Julie Streng, 40, of Greensboro, N.C. But Proteau, a prosecutor for the British Columbia Ministry of Justice who is six months pregnant with her first child, birdied the final two holes of regulation, including a clutch 4-footer on 18 to square the match. She completed the comeback with a two-putt par on the first extra hole.

“Pregnant or not, that would have been a stressful round of golf, a tiring round of golf. It was a really tough match and Julie made some great putts,” said Proteau, who reached the Round of 16 in 2013. “I played the last three holes really, really well. Thankfully it didn’t go any longer.”

Four-time champion Meghan Stasi made the first step in her quest for a record fifth Women’s Mid-Amateur title. Stasi, 36, of Oakland Park, Fla., won the final three holes en route to a 4-and-2 win over Lisa McGill, 55, of Philadelphia.

“I had a bunch of bogeys, but I just learned a bit more about the course,” said Stasi, who last won in 2012. “I played solid, but I made a few mistakes. I definitely need to go out and work on a few shots.”

Should Stasi win this week, she would join a short and illustrious list of players who have won the same USGA championship at least five times: JoAnne Gunderson Carner (five U.S. Women’s Amateurs), Carolyn Cudone (five U.S. Senior Women’s Amateurs), Bob Jones (five U.S. Amateurs) and Glenna Collett Vare (six U.S. Women’s Amateurs).

Of the five Indiana players who qualified for the championship, three reached Tuesday’s Round of 32. Cara Stuckey, 34, of Terre Haute, never trailed in her 2-and-1 win over Renata Young, while Tobi Herron, 36, of Columbus, won the first six holes and cruised to a 5-and-4 victory over Therese Quinn. Potter rounds out the victorious Hoosier trio, while Plainfield’s Julie Carmichael and Noblesville’s Lisa Cook were eliminated.

Stuckey and Herron will meet in the Round of 32. The winner of that match will face Shirley or Cornett in the afternoon Round of 16.

Mina Hardin, the 2010 U.S. Senior Women’s Amateur champion, advanced with a 2-and-1 win over Daria Cummings, while 2009 Women’s Mid-Amateur champion Martha Leach fell, 2 up to Jane Chin.

Editor's Note: Lynne Cowan of AmateurGolf.com won her round of 64 match 1-up over Kathy Crumley of Texas.

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.