Australian Stosur accounted for Elina Svitolina in straight sets, winning 7-6 (8-6) 6-2 in the semi-finals at the Utsubo Tennis Center in Osaka.
Stosur - winner of last year's event in three sets against Eugenie Bouchard - was on court for an hour and a half against the third-seeded Ukrainian as she moved to within one win of back-to-back triumphs in Japan and her third in total, having taken out the inaugural edition in 2009.
As expected, the opening set was evenly contested in the pair's first-ever meeting.
Stosur's serve worked against her early, registering four double faults and going at just 22 percent on her second serve.
But the 30-year-old still managed to pull her game together and take the lead via a tie-breaker.
That shootout seemed to unsettle Svitolina, who faded in the second set.
Stosur flexed her muscles, sending down three aces as she cruised to victory.
Next up for Stosur is fifth-seeded Kazakh Zarina Diyas.
Diyas got the better of Thailand's Luksika Kumkhum 6-2 7-5 in Saturday's early semi-final.
The 20-year-old wrapped up proceedings in a little over an hour as she progressed to her first WTA Tour final.