Czech left-hander Petra Kvitova reached the French Open quarter-finals for the first time in eight years as she overpowered China's Zhang Shuai 6-2 6-4.

On yet another chilly day in the French capital, seventh seed Kvitova's superior firepower proved decisive as she posted her fourth successive straight-sets victory.

With so many big names already out, Kvitova will sense a golden title opportunity as she heads into a quarter-final against either Germany's Laura Siegemund or Spain's Paula Badosa, neither of whom are seeded.

The 30-year-old Czech, who reached the semi-finals in 2012, made her intentions clear from the start as she seized on anything short to dominate from the baseline, moving 4-0 ahead in 15 minutes on Court Philippe Chatrier.

Zhang, in the fourth round of a Slam for only the third time in 33 attempts having also not dropped a set so far, finally began to dig her heels in as Kvitova's error-count increased but she was unable to turn the tide.

Kvitova had to wait around in the cold as Shuai took a medical timeout at the end of the first set, but she turned up the heat to get an early break in the second set.

She broke again to lead 5-2 but some wild errors allowed Zhang to win two straight games and create some tension.

Unseeded German Laura Siegemund came through a tight opening set before cruising past Spaniard Paula Badosa 7-5 6-2 to reach her maiden Grand Slam quarter-final at Roland Garros

Both players struggled on serve in the opening set of their see-sawing fourth-round meeting on Court Simonne Mathieu, before Siegemund switched gears at 5-5 to claim the decisive break and take the early advantage in the contest.

Badosa, a former junior champion who knocked out 2017 winner Jelena Ostapenko in the previous round and 2018 runner-up Sloane Stephens in her second match, found herself down 3-1 in the second set as Siegemund turned up the heat.

World nummber 66 Siegemund fought off a spirited comeback attempt from Badosa to stretch the lead further with a break in the seventh game of the second set, before closing out her victory in style.

Up next for Siegemund is a meeting with Kvitova.

American fourth seed Sofia Kenin appeared to be unnerved by the cheers of the sparse partisan crowd as she recovered from a wobbly start to reach the last eight with a 2-6 6-2 6-1 victory over France's Fiona Ferro. 

The Australian Open champion, who next faces compatriot Danielle Collins or Tunisian Ons Jabeur, broke into tears after ending the contest with a service return winner. 

She complained that the crowd had been unfair to her. 

"The crowd wasn't the best, which is understandable, but still I wish it would have been a little bit different," she told a news conference. 

"I tried to use that as motivation. Obviously I was not really too happy with how it was going. I knew it's expected. I understand why. I'm playing a French player, and she's had a great run here." 

A maximum of 1,000 spectators are allowed per day at Roland Garros amid Covid-19 restrictions, and some 500 attended the match on court Philippe Chatrier, voicing their support for Ferro.