(USGA/Chris Keane)

Shirley, 27, of Roswell, Ga., cruised to a 5-and-4 win over Andrea Kraus in the morning quarterfinals. In her semifinal match against four-time and defending champion Meghan Stasi, she made a stirring comeback. Two down with two holes to go and having never held the lead, Shirley stormed back to eliminate Stasi in 19 holes.

Stroke-play medalist Potter, 25, of Granger, Ind., was behind for only one hole in her two Wednesday matches. She held the lead throughout her 3-and-2 quarterfinal victory over Tara Joy-Connelly, and only trailed Stefi Markovich for one hole en route to a 3-and-2 win.

The 2013 U.S. Women’s Mid-Amateur Championship is open to female amateur golfers who have reached their 25th birthday by Oct. 5. It consists of 36 holes of stroke play followed by six rounds of match play, with the championship scheduled to conclude with an 18-hole final 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.

Shirley never led in regulation and trailed for all but three holes of the semifinals, as Stasi first took the lead with a par at the par-4 second. But Shirley hung close, never letting Stasi extend her advantage beyond two holes.

Stasi earned a 2-up lead with two to play when Shirley’s approach at the par-4 16th sailed long and trickled down the greenside slope.

“I was licking my chops after I struck that ball because I struck it so good,” said Shirley, who failed to reach the green with her chip, leading to a double bogey and a 2-down deficit. “I don't know if it was adrenaline and that's why it carried farther than it should have.”

But Shirley capitalized on the struggles that have plagued Stasi over the final two holes throughout the championship. Following Stasi’s bogey at the par-4 17th, Shirley drained a 7-footer to pull within one. Stasi then sailed her approach at the par-18th far right of the green and failed to get up and down, settling for bogey. Shirley was faced with a tricky 18-foot putt for birdie.

“My dad (William, her caddie) said this is going to be fast, so I played it off the heel and tried to get it down there to a tap-in,” said Shirley, a 2008 graduate of Auburn University. Her father’s advice helped Shirley gain the tap-in par she needed to send the match to the 19th hole.

Stasi’s approach at the 19th found the creek in front of the green. With Shirley’s birdie putt safely on the green, Stasi’s putt for bogey came up short, and the four-time champion conceded the victory.

“I hate that Meghan finished that way because she played so well all day, but that's match play,” said Shirley, a manager of Rules and competitions for Atlanta Junior Golf. “There's a reason she's won four of these. She's got one of the best short games I've ever seen. I'm just lucky to come away with the win today.”

“I beat myself up today on a few shots,” said Stasi, who is now 34-4 in Women’s Mid-Amateur match play. “Just really stupid mistakes and I know better. It’s a shame, but she played solid and she did what she needed to do.”

After playing well on the inward and outward nines at Biltmore Forest in different rounds, Potter finally assembled the complete performance she has been seeking. She took her first 2-up lead over Markovich with a birdie at the par-5 seventh, a moment she pointed to as the turning point of the match.

“I'm staying with somebody who plays on this golf course and they had told me the entire time, always hit to the front of the green. It's going to roll back,” said Potter, a 2011 graduate of the University of Missouri. The advice was solid, as Potter hit it to 8 feet and converted the birdie.

Potter took the victory at No. 16 when Markovich struggled on and around the green. Tears filled Potter’s eyes when she realized what she has already accomplished this week.

“I came in with the goal of giving myself a chance of winning this championship and now I've done it,” said Potter, who, like Shirley, has her father, Phil, at her side as caddie this week. “It just hit me right now that I've gotten to this place and how rare that is for a golfer. That's huge for me.”

This will be the third time in championship history that the final match will include two players in their 20s, including the 1993 and 1994 finals. Should Potter win, she will be only the second 25-year-old to win the championship, joining Sarah LeBrun Ingram in 1991. Potter could also become the USGA’s sixth left-handed champion overall and first left-handed female champion.

The winner will receive a 10-year exemption in the U.S. Women’s Mid-Amateur, while the runner-up will receive a three-year exemption.