The 27-year-old put forth a breathtaking display of power tennis, rebounding from an early deficit to storm past No.3-seeded Garbiñe Muguruza, 7-6 (3), 6-3, to reach her 10th career Grand Slam quarterfinal and second in NY.
Kvitova has knocked off third seed Garbine Muguruza 7-6 (7-3) 6-3 in the fourth round of the US Open.
The twice Wimbledon champion stayed composed while Muguruza grew increasingly nervous, challenging line calls with no apparent reason as Kvitova moved her left and right with her crafty left hand.
It was the most significant match since Kvitova's comeback from the horrendous hand injuries she suffered when she was stabbed by an intruder at her home last December.More news: Ruud van Nistelrooy hails Manchester United and Romelu Lukaku
Muguruza, one of the pre-tournament favourites, dropped serve once.
The Top Seeds are back in action in NY today, with Rafael Nadal and Karolina Pliskova both aiming to reach the quarter finals.
Even with the loss, Muguruza could be No. 1 if the other players lose before the final.
The 27-year-old, who next faces Venus Williams, insisted she will continue to play with no expectations but also without being surprised by what she can still produce.More news: Frankfurt starts defusing massive WWII bomb after evacuating 60000
"She's one of the biggest hitters and a talented player". "I think she's playing very well".
Her team in the players' box have been wearing T-shirts which have printed on the front "Courage, Belief and PJD with a heart between the P and the J. In Czech it means "C'mon". This was my best match, so I was happy to see my level rise as the tournament is continuing, because I know my opponents are going to be better; I need to be better.
Kvitova has won four of her previous five matches against Williams. "If people think I could be a good competitor there and go far, that's fine". Williams has seven Grand Slam singles titles but hasn't won in Flushing since 2001.
Muguruza found Kvitova's form astonishing considering what she has been through.More news: Virat Kohli hits 30th ODI century, joint second highest in cricket history
"What she's gone through is unimaginable, unreasonable", Williams said. After playing at Roland Garros and Wimbledon, Kvitova is only playing in her eighth tournament of the year at the U.S Open. "To be able to come out here and do what she needs to do, to clear her head, it's such a handsome thing to see".