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 have 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.
Kvitova regained her focus though to seal victory with a love service hold.