The 13th-seeded Czech left-hander, in only her eighth event of the year after hand surgery following a knife attack by a home intruder last December, will play for a semi-final berth Tuesday against seven-time Grand Slam champion Venus Williams.
“I worked hard to come back and be here,” Kvitova said. “It means a lot.”
Kvitova, whose All England crowns came in 2011 and 2014, said after her victory in Arthur Ashe Stadium that her journey back from the attack has been a difficult climb.
“I don’t have words to describe,” she said. “It was a tough time. All five months were very tough. It was just a journey I didn’t know how it would end.
“If it ends here on the big stage it’s a happy end.”
Kvitova, whose first event this year was the French Open, has a new appreciation for her chances at Grand Slam glory.
“Every moment I’m living right now is something special,” Kvitova said. “I know having these moments it’s even better than before.”
Muguruza remains ahead in a three-woman fight for world number one after the US Open but can be overtaken by Czech current number one Karolina Pliskova if she makes the final or Ukraine fourth seed Elina Svitolina if she reaches the semi-finals.
Results from day 7 of the US Open on Sunday (x denotes seeding):
Sam Querrey (USA x17) bt Mischa Zverev (GER x23) 6-2, 6-2, 6-1
Kevin Anderson (RSA x28) bt Paolo Lorenzi (ITA) 6-4, 6-3, 6-7 (4/7), 6-4
Pablo Carreno-Busta (ESP x12) bt Denis Shapovalov (CAN) 7-6 (7/2), 7-6 (7/4), 7-6 (7/3)
Diego Schwartzman (ARG x29) bt Lucas Pouille (FRA x16) 7-6 (7/3), 7-5, 2-6, 6-2
Venus Williams (USA x9) bt Carla Surez Navarro (ESP) 6-3, 3-6, 6-1
Petra Kvitova (CZE x13) bt Garbine Muguruza (ESP x3) 7-6 (7/3), 6-3
Sloane Stephens (USA) bt Julia Goerges (GER x30) 6-3, 3-6, 6-1
Anastasija Sevastova (LAT x16) bt Maria Sharapova (RUS) 5-7, 6-4, 6-2