New York, Sep 4 (IANS): Eight months ago, Petra Kvitova of the Czech Republic wasn't sure she'd be able to hold a tennis racket again. Now the tough woman is in the quarter-finals of the US Open.

The 13th-seeded Kvitova, battling back after a home-invasion knife attack last December, upset third seed Garbine Muguruza on Sunday night, winning at 7-6(3), 6-3 to advance to the US Open last eight for the second time in her career, reports Xinhua news agency.

Muguruza came out firing and built a 4-1 lead over Kvitova. But the Czech battled her way back, saving a break before fighting to take the first set 7-6(3) in 64 minutes.

In the second set, 2017 Wimbledon champion Muguruza seemed as though she could not recover from the tough tiebreak. Kvitova continued to dominate and closed out the win in one hour and 45 minutes.

Kvitova was 4 for 7 on break points and finished with 24 winners and 42 unforced errors, while Muguruza was 3 for 12 on break points and finished with 7 winners and 25 unforced errors.

Kvitova has yet to drop a set at the US Open and would need to reach the semifinals to have a chance of returning to the Top 10.

"I came here without any expectations," Kvitova said. "I'm really enjoying it more than before."

Kvitova will play seven-time major champion Venus Williams of the United States on Tuesday with a semi-final berth at stake. Serena, seeded No.9, beat Carla Suarez Navarro from Spain 6-3, 3-6, 6-1 earlier on the day.

Kvitova still hasn't quite regained full strength in her left hand, the one operated on after being cut by an intruder at her home in the Czech Republic in December.

"Given all she's been gone through, playing at this level is remarkable," Muguruza said.

Kvitova returned to the tour in late May at the French Open.

"I don't think that I can find the right words. It was a difficult time," Kvitova told the Arthur Ashe Stadium crowd after beating Muguruza. "I didn't know how the journey would end."