Osaka went on to hold, and earned two set points in the following game, which Kvitova saved.
Fittingly, the set progressed to a tiebreak, which Osaka dominated, blazing three winners to build an insurmountable 5-1 lead.
She had the first set in her grasp, a crucial outcome; Osaka had won her past 59 matches after snaring the first set. And this was the first set Kvitova had dropped all fortnight in Melbourne.
The Czech responded strongly, bludgeoning two forehand winners on her way to breaking serve in the opening game.
Yet from 2-0 down, Osaka won four straight games to wrest control of the set, the force of her returns beginning to wear down Kvitova, whose game was now leaking errors.
That pattern repeated in the ninth game; Osaka crushed a return down the court at Kvitova who could not control the shot. Kvitova sent it long to go down 0-40, and Osaka held three championship points.
Here, the match dramatically turned. Kvitova saved the first with a winner, and Osaka suddenly started missing her returns.
She had a chance to serve out the match when 5-4 up, but double-faulted to fall behind 15-40. Another error saw Kvitova break serve and level at 5-5.
From 3-5, 0-40 down, Kvitova would reel off 23 of the next 27 points against Osaka, whose game and emotions were completely unravelling.