With the victory, Higgins, 52, supplanted Carol Semple Thompson, who won the championship at age 48 in 1997.
I'm still in shock, said Higgins, a quarterfinalist in 2007. I really am. I just can't believe it. Last night in bed I was tossing and turning all night, saying, You could be a national champion, don't think about it, don't think about it because it's probably not going to happen. She's probably going to go out and clean your clock.
Higgins won the first hole and never trailed in the 18-hole match at Barton Hills Country Club, which also hosted the 1998 U.S. Womens Amateur.
Bunker trouble on the sixth hole forced Higgins to concede it, which squared the match. That status lasted for four holes.
The match was all square through nine holes but was Higgins was steady on the inward nine, missing just one green.
I knew I had my work cut out for me, said Simmons, 40. She doesnt make a lot of mistakes.
Simmons found the bunker on the par-3 11th and could not save par to give Higgins, a former tennis player at the University of Wisconsin, a 1-up lead.
Higgins, who employed Ken Hartmann, the Golf Association of Michigans director of Rules and competitions as her caddie, then three-putted the 14th hole to square the match.
The longer hitting Simmons, the owner of a personal fitness business, then missed the green on the 15th short with a poor iron shot and could not save par. Higgins, a mother of two sons, two-putted to win the hole for a 1-up lead.
Simmons missed an opportunity to square the match on the par-5 17th, when her 12-foot birdie putt came up short. Both players missed birdie putts to halve the 18th hole.
The finalists, both playing in their seventh Womens Mid-Amateur, coincidentally played together in the stroke-play portion of the championship.
We became fast friends, Higgins said.