China's Peng Shuai reached the first Grand Slam singles quarterfinal of her career on Sunday, toppling 14th-seeded Lucie Safarova 6-3, 6-4 to reach the US Open last eight.

Peng, who had five Grand Slam fourth-round appearances on her resume but had never cracked the quarterfinals, fired nine aces past her Czech opponent - including one on match point to seal the win after one hour and 11 minutes.

"I don't know how many aces I had but I know I had one on the match point," said Peng, who had lost four of five previous encounters with Safarova.

"Amazing! I'm so happy, so excited," the softly-spoken Tianjin native said. "All the time in Grand Slams I think maybe I can take one more step, one more step."

She converted both of her break opportunities - one in each set - and saved the only break point she faced in the contest, which was played under the lights on the intimate confines of Court Five after a two-hour rain delay forced the day's late afternoon matches to be rescheduled.

She said she was preparing for her match as usual and had not even noticed the torrential rain sweeping across the tennis center at Flushing Meadows until she saw the match on court before hers had been suspended.

That bit of confusion did not seem to slow the 28-year-old down, she fired 17 winners with just seven unforced errors, giving Safarova no openings.

She was astonished to see so many Chinese fans in the stands of the 1,032-seat Court Five.

"My fitness coach, he's from France, and he said 'I thought you were playing in China'," said Peng, who is carrying Chinese hopes with Australian Open and former French Open champion Li Na sidelined by injury.

The world No 39 owns two Grand Slam doubles titles and is through to the third round of the doubles with partner Hsieh Su-wei of Chinese Taipei.

Now she will have to learn to manage both competitions in the second week of a major - a problem she is happy to have.

"I just need more rest, more focus," said Peng, who will face Swiss teenager Belinda Bencic for a place in the semifinals.

It promises to be a scintillating match-up of the world's No 1 ranked doubles player and former world No 1 junior player Bencic, who won the girls' titles at last year's French Open and Wimbledon.

Bencic's 7-6 (6), 6-3 victory over No 9 seed Jelena Jankovic of Serbia marks her best Grand Slam showing and made her the youngest US Open quarter-finalist since Martina Hingis won the title in 1997.

That connection was all the more relevant as Hingis was in Bencic's player's box cheering her on as a regular practice partner of the Swiss teen, who is partly coached by Hingis' mother, Melanie Molitor.

"It was always a dream to play on this court," Bencic told the crowd at Arthur Ashe Stadium. "I watched it as a kid and I always dreamt about playing here."

"I was overwhelmed for the first time, the first games," she said. "It was just everything so huge and I had to get used to it."