Chinese tennis player Peng Shuai serves to Lucie Safarova of the Czech Republic at the US Open on Sunday (US time) in New York City. Photo: AFP

On a day of shocks at the US Open, Chinese tennis player Peng Shuai reached the first Grand Slam singles quarterfinal of her career on Sunday (US time), toppling 14th seed Lucie Safarova 6-3, 6-4 to reach the 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.

"Amazing! I'm so happy, so excited," said Peng, who had lost four of five previous encounters with Safarova. "All the time in Grand Slams I think ­maybe I can take one more step, one more step."

She was astonished to see so many Chinese fans in the stands of the 1,032-seat Court 5 at the USTA Billie Jean King National Tennis Center.

"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 28-year-old world No.39 owns two Grand Slam doubles titles, and is through to the third round of doubles in New York City with Chinese Taipei's Hsieh Su-wei.

Now she'll have to learn to manage both competitions in the second week of a ­major - a problem she's happy to have.

She will face Swiss ­teenager ­Belinda Bencic for a place in the semifinals.

Peng also eliminated fourth seed Agnieszka Radwanska of Poland in the ­second round and 28th-­seeded Roberta Vinci of Italy in the third.

Baking heat, rain and the threat of lightning all forced stoppages in play on Sunday but Roger Federer and Caroline Wozniacki marched on through a day of wild weather and upsets.

Former world No.1 Wozniacki had her fourth-round match with Maria Sharapova halted briefly by the heat rule but it was the fifth-seeded French Open champion who wilted under a blazing sun, falling 6-4, 2-6, 6-2.

Later, rain interrupted Federer's clash with Marcel Granollers before the five-time US Open champion came back from a set down to crush the Spaniard 4-6, 6-1, 6-1, 6-1 and storm into the fourth round.

Gilles Simon and Spanish fourth seed David Ferrer sweated it out under a midday sun, the 26th-seeded Frenchman posting the first big surprise in the men's draw with a 6-3, 3-6, 6-1, 6-3 win.

A stormy day finished off with another upset on Arthur Ashe Stadium as 17-year-old Swiss sensation Bencic swept past ninth-seeded Serb and former world No.1 Jelena Jankovic 7-6 (8/6), 6-3.

The departures of Sharapova and Jankovic leave only world No.1 Serena Williams, Canadian seventh seed Eugenie Bouchard and Wozniacki as the surviving members of the women's top 10.