Thompson, of Sewickley, Pa., beat Carr, 2 and 1, for her 28th straight match-play victory in the event.
Thompson will face Nancy Fitzgerald of Carmel, Ind., a 1-up winner in 19 holes over Jo-Ann Lindsay of Edina, Minn., in Thursday morning's semifinals.
'Tomorrow could be a very special day, but I'm trying not to think about it because it gets in the way of me playing the golf course,' Thompson said.
In the other semifinal, Marlene Streit of Toronto, who beat Carolyn Creekmore, 2 and 1, will face Marianne Towersey of Newport Beach, Calif., who defeated Pat Milton of Munroe Falls, Ohio, 6 and 5.
The loss punctuated a highly emotional week for Carr, who found out five days before arriving at the tournament that she had breast cancer.
'You know, I really haven't had a chance for a good cry yet,' Carr said. 'Still, I came here to play golf and not worry about it because I don't know anything more than I did when I got here.'
Streit, the 1956 U.S. Women's Amateur champion, won the senior women's amateur twice when it was contested as a stroke play event in the early 1990s.
The 18-hole final is set for Thursday afternoon.
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