Seventh seed Sharapova defeated world number one Caroline Wozniacki 7-5, 6-3 in a match littered with service breaks.
Earlier Stosur had steam-rollered China's Li Na 7-6 (8/6), 6-0.
Sharapova rolled back the years with a performance of crisp power hitting to eventually prove too much for her Danish opponent.
She broke Wozniacki early on but when she led 4-3 there were four breaks in a row until the Russian finally held serve to take the set 7-5.
The service struggles continued at the start of the second set as four of the first five games went against the server.
That saw Wozniacki open up a 3-1 lead but Sharapova wouldn't let her consolidate and reeled off the final five games as she consistently found the corners with rasping ground-strokes.
The 27-year-old Stosur recorded her third straight sets win over Li and maintained her unbeaten record against a player ranked one place above her in the world.
Stosur also reached her first final since the 2010 French Open almost a year ago.
And she said that there was nothing unusual about Li's second set collapse.
"Sometimes when that happens, if you do win a tight first set then it can be a real boost to that person but for the other person that loses it can almost be a deflation and it's a big disappointment," she said.
"But I guess this is when you have to be tough enough to try and forget about it and start over again because obviously you have been playing well enough to play a tight first set.
"Sometimes it is probably more a question of the mentality of going into the second set because there must be something that's been going okay if you've had a tight first set.
"That does happen a lot in tennis, both men's and women's and I guess it is every player's job to not let it happen but sometimes it does."
The sixth seed got off to a flying start and broke Li in the opening game, working the Chinese wide to her backhand and forcing a short defensive return before steaming up to the net and powering away a forehand winner.
Stosur forced a set point on the fourth seed's serve at 5-3 but a deep first serve gave Li a short return to put away.
A series of deep crosscourt backhands setting her up for a forehand winner from close to the net saw Li fend off another set point soon after before she held serve.
That proved a vital hold as in the next game Li forced a break point and levelled up at 5-5 when Stosur went wide with a backhand.
The first mini-break in the tie-break went Li's way when she brought Stosur up to the net with a drop shot and then rasped a backhand pass crosscourt.
But she gave it up immediately with a double fault.
Li brought up a set point with a forehand winner down line but couldn't take it when she put the same shot into the tramlines on the next point.
Stosur was not so generous when she was presented with a set point moments later, hitting a powerful serve out wide and following it up with a forehand winner.
The world number seven got off to a quick start in the second set as well as Li double faulted on break point in the second game.
And the Chinese player's game crumbled from there as Stosur cantered through the rest of the set.