Azarenka, just three days past her 24th birthday, defeated seventh-seeded Serbian Ana Ivanovic 6-0, 4-6, 6-3.
Stosur battled back from a 0-4 first-set deficit en route to a 7-6 (7/2) 6-3 victory over France’s Virginie Razzano.
Azarenka, the two-time defending Australian Open champion, showed no sign of the right knee injury that forced her out of Wimbledon after the first round.
Ivanovic, like Azarenka a former world number one, rallied after failing to win a game in the first set. But Azarenka gained a pivotal break at 2-2 in the third and went on to secure her third straight victory over the Serbian.
“It was an interesting match,” Azarenka said. “The first set, the score definitely doesn’t tell the whole story because there was a lot of close games. In the second set I missed couple easy shots and she was right there to take those opportunities. I thought I let her into the match.
“But she came up with great stuff. I have to give her credit. She started serving well, going for her shots. But when I analyze my match, I analyze about my game, not what my opponent did. The note that I am going to take from that is I have to keep going the same way that I was playing in the first set — taking my opportunities, going for my shots, making some moves, taking the ball forward. I’m just happy with the end result, that I was able to overcome some things and still find the way to win. That’s the most important.”
Azarenka will be seeking a 17th career title, and third of the season, when she takes on Stosur, the 2011 US Open winner.
Stosur, meanwhile, has reached her first final of the season, and will be vying for her first title since her US Open triumph. History is not on her side. She has never beaten Azarenka in eight career meetings.
Razzano, who had needed three hours and 35 minutes to get past third-seeded Petra Kvitova on Friday, took a break and left the court after dropping the first-set tiebreaker to Stosur.
However, she couldn’t find the spark she needed, and once Stosur had broken in the third game of the second set the Australian cruised home.