Radwanska had beaten Cornet in straight sets in all three of their previous meetings, and things looked headed the same way this time as she raced through the first set at love - not even facing game point in any of those six games - and, after losing the second set, jumping out to a 3-0 lead in the third.
The No.1-seeded Radwanska even had a point for a 4-0 in the decider but the No.4-seeded Cornet never stopped grinding, winning six of the last seven games of the match to scrape it out, 06 62 64.
"It was an epic match today against Aga and a great win for me at the end," Cornet said after the match. "I'm already playing my second final of the year at the beautiful tournament in Katowice, and I'm enjoying my time so much here. I can't wait to be on court again tomorrow trying to go for the title!"
Cornet's breakthrough year against top players continues - going into Dubai two months ago she was a dubious 0-17 lifetime against Top 4 players but finally got on the board there with a semifinal win over World No.1 Serena Williams. The Frenchwoman now has a second Top 4 win over the World No.3.
She's also through to her eighth WTA final now, going 3-4 in her first seven - her three WTA titles all came at the International level, at Budapest in 2008, Bad Gastein in 2012 and Strasbourg in 2013.
Awaiting her will be Giorgi, who kept her dream week going with a 76(2) 64 upset over No.3 seed Carla Suárez Navarro. The two put on a serving display in the first set - no breaks, not even any break points. But Giorgi opened up a 3-1 lead in the second set and the two kept holding serve until Giorgi won.
"It was a tough match," Giorgi said. "It wasn't easy. I wasn't playing really well, and neither of us were that consistent today, but I tried my best and I think I was just a little bit better in the end.
"I played well on the important points today."
Giorgi, who had never even been to a WTA quarterfinal before this tournament, is now through to the first WTA final of her career. And with wins over No.16-ranked Roberta Vinci and No.17-ranked Suárez Navarro this week, this is also just the second time the Italian has beaten two Top 20 players in the same tournament - she defeated both Flavia Pennetta and Nadia Petrova at Wimbledon in 2012.
And what about reaching her first WTA final? "I'm pretty happy!" she added.
Cornet beat Giorgi in their only previous meeting, at this year's Australian Open, though it was about as close as could be - Cornet rallied from 4-1 down in the third to win in two hours and 36 minutes.