Kvitova, who’d sprayed 19 unforced errors, settled into an arm wrestle for the second set, which saw break points fly thick and fast in all but one game as both players grappled for timing and confidence on big points.
Kvitova finally made the critical break for 4-3, turning the match her way as the pressure of pushing ahead in virgin territory told on the 24-year-old. After no less than seven Grand Slam exits in the third round, including here last January against Ash Barty, Sakkari was striving not just for a first major quarterfinal but the first for a Greek woman. It was a feat that eluded her mother, former WTA pro Angeliki Kenellopoulou, who watched nervously from the player’s box.
Finally gaining an easy hold for 5-3, Kvitova was looking like her old shot making self as she powered to 3-0 in the third, winning six straight games and savaging the Sakkari serve with withering returns.
The “Sakk attack” that so animated the Greek chorus was blunted; the tentative, struggling Kvitova of the first set long gone. Unplayable Petra was back.
Ahead for Kvitova is a same-time-next-quarterfinal rematch with No.1 seed Ash Barty, or No.18 seed Alison Riske.