Thompson, of Sewickley, PA, extends her USGA record of winning the most consecutive matches in a single championship to 22. Thompson will now face Anne Carr of Seattle, Wash. in the semifinals.
Thompson started Wednesday's match quickly by gaining a 2-up lead after five holes. She reached that point with a par at the fourth and a birdie at the fifth.
With her lead at 4-up through 14, Thompson secured the win with a 12-foot birdie putt on 15. Fitzgerald had a chance to extend the match on the par-5, but her five-footer didn't find the cup.
'I'm amazed. I don't feel as though I've played that well all week,' said Thompson, who is looking to become the first medalist to win the championship since it switched to match play in 1997. 'I love playing with Nancy. She's one of the best players.'
Fitzgerald, the 1997 champion, had downed Alice Harcourt, 3-and-2, to reach the quarterfinals.
Carr moves into the semifinals with her 3-and-2 win over Connie Shorb. This will be a rematch of last year's final when Thompson defeated Carr 1-up.
'Well, I am ready for Carol,' said Carr. 'It's anybody's ballgame tomorrow. Whoever has their best game is going to win.'
The other semifinal pits Barbara Berkmeyer against Marsha Butler. Berkmeyer, from St. Louis, Mo., advanced with a 5-and-4 victory over Alison Murdoch, this year's Canadian Senior Amateur champion. Berkmeyer had been 5-up after nine holes, before closing out the match on the 14th.
Butler, a San Diego-native, conquered Taffy Brower 3-and-2. Butler grabbed a 1- up lead on the ninth when she chipped in from 30 feet. She built her advantage to 3-up before Brower conceded on No. 15, giving Butler the victory.