Roger Federer, of Switzerland, stretches for a volley against Marcel Granollers, of Spain, in the third round (Source: AP)

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

Former world number one 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 U.S. 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 court as 17-year-old Swiss sensation Belinda Bencic swept past ninth-seeded Serb and former world number one Jelena Jankovic 7-6 (6) 6-3.

“It was always a dream to play on this court,” said Bencic, who is coached by Martina Hingis’s mother Melanie Molitor.

“I watched it as a kid and I always dreamt about playing here.”

Next up for Bencic is another giant-killer in China’s Peng Shuai. The doubles specialist eased into the last eight with a 6-3 6-4 win over 14th-seeded Czech Lucie Safarova.

The departures of Sharapova and Jankovic leave only world number one Serena Williams, Canadian seventh seed Eugenie Bouchard and Wozniacki as the surviving members of the women’s top 10.

MARATHON TRAINING

Wozniacki showed great grit in battling past Sharapova as the punishing conditions turned the match into a battle for survival.

A grand slam title is the one major hole in Wozniacki’s considerable resume and the Dane may never have a better opportunity to fill it with the draw having opened up.

The 2009 U.S. Open runnerup is training to run the New York marathon later in the year and appeared better equipped to cope with the soaring temperatures and stifling humidity that took the players off court.

After play resumed, Wozniacki turned up her own heat on the five-time grand slam winner in the third set.

“I think it will help me a lot,” said Wozniacki, who will next face 13th seed Sara Errani, a three-set winner over Croatian Mirjana Lucic-Baroni. “Today was a tough battle out there. It was humid. It was hot. I had to change my dress.

“That rarely happens. It was just soaked. Definitely (the training) is helping, because I felt fresh out there and I felt like I could keep going.”

The Dane captured the decisive break in the third game after a spectacular point in which she raced three times across the baseline to retrieve shots before the Russian netted a backhand volley to fall behind 3-1.

Wozniacki broke Sharapova again for good measure in the final game to return to a grand slam quarter-final for the first time since the 2012 Australian Open.

Barring Ferrer’s upset, the men’s top 10 seeds remain intact, with sixth seed Tomas Berdych and seventh seed Grigor Dimitrov both advancing.

Rising talent Dominic Thiem continued to surprise, following up his second round win over 11th seed Ernests Gulbis by dismantling 19th seed Feliciano Lopez of Spain 6-4 6-2 6-3.

The 20-year-old Austrian will have to pull a bigger upset out of his hat in the next round when he meets Berdych, a straight sets winner over Russia’s Teymuraz Gabashvili.

Gael Monfils mowed down 12th seed and fellow Frenchman Richard Gasquet 6-4 6-2 6-2 and will also need to produce something special to overcome Dimitrov, who recovered from a sleepy start to dump Belgian David Goffin 0-6 6-3 6-4 6-1.