The ninth-ranked Williams edged the tenacious Czech to have a shot at her second title of the season. Azarenka has won four tournaments this year.
"Victoria has been so consistent in her game this year," Williams said. "She is so consistent, so amazing and so, just nearly perfect. I am going to the final with nothing to lose."
Williams holds a 6-1 head-to-head record against Azarenka, whose only win came in 2009. This will be the first time they meet on clay.
"She's one of the best players in the world and one of the toughest opponents to play against so we'll see," Azarenka said. "But as I said, it's going to be a different story."
While both Nadal and Novak Djokovic promised to never play again on the blue clay, neither women's star saw their big-hitting style overly hampered by the surface many players have called slippery.
Williams held off Hradecka's seven early aces in a first set, which she won in a tiebreaker. She then broke Hradecka three times in the second to cruise to her 12th consecutive win on clay this season.
"She just did everything really well and I was able to come through in the tie break," Williams said. "After that I was able to relax, to make less errors and make more shots and be more aware out there."
The 105th-ranked Hradecka had upset defending champion Petra Kvitova and U.S. Open winner Sam Stosur to reach the semifinals.
Azarenka had little trouble beating Radwanska for the sixth straight time.
Azarenka hit a deep return to set up a slam and break her Polish opponent's first service game, and went on to hit 14 winners and held at love to wrap up the first set. The players traded a pair of breaks in the second set before Azarenka, the runner-up last year, won a decisive third break with a crosscourt return.
"I'm really happy. All the top players are here and I'm in the final and looking forward to it," said the 22-year-old Belarusian. "[Radwanska and I] keep meeting each other. I'm glad to win today. The score maybe wasn't so close, but it was a good match."