But the vocal NY crowd will likely throw its support behind the American, who won the tournament in 2000 and 2001.
Sharapova hadn't played in a major tournament since the Australian Open in January 2016, when she tested positive for the newly banned drug meldonium. "I'm very grateful that I can be part of it again", Kvitova said.
The former two-time Wimbledon champion was only able to make it to the second round before being knocked out by unseeded Madison Brengle but the simple fact she was involved in the Grand Slam proved another major step. It took me a while to find it.
And she's doing all this six years after being diagnosed with an auto-immune disease that dropped her ranking to as low as No.137 in 2012.
Kvitova, 27, admitted to nerves in the final game, where she had to save three break points, before roaring herself to victory. "It's very unfortunate but at the same time I'm happy to be in the fourth round".
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The weather has been on her side, with none of New York's normal late summer humidity, which has badly affected Kvitova in the past. So probably in my mind was just there, thinking about it.
"I came here without any expectations", the 13th-seeded Kvitova said. She, the world No. 14, has just won 7-6 (7-3), 6-3 against world No. 3 Garbine Muguruza, who is now the best player in women's tennis - best player and No. 1 are not always the same - and had won 19 of her last 21 matches.
The Czech was sidelined for five months after being stabbed in her left playing hand by an intruder at her home and although the 13th seed has gradually moved towards her best level, Muguruza was the hot favourite under the lights at Arthur Ashe Stadium.
The physical and mental torment seemed to be completely non-existent as Kvitova then won the Aegon Classic a month later, in only her second tournament since returning to the Tour.
After saving match point in her third-round meeting with Zhang Shuai, the world number one needed just 46 minutes to beat Jennifer Brady 6-1 6-0. As she said once: "Respecting my opponent has always been important to me because without an opponent we can't play this handsome game". "She has a great timing and a lot of power, for sure". In the other quarter-final in the bottom half of the draw the American Sloane Stephens will face Anastasija Sevastova after the Latvian ended Maria Sharapova's run in the tournament. The 37-year-old Williams, who won the title in 2000 and 2001, got to the quarterfinals by beating Carla Suarez Navarro 6-3, 3-6, 6-1. In the quarters, Carreno Busta will play No. 29 Diego Schwartzman of Argentina, while No. 17 Sam Querrey of the United States takes on No. 28 Kevin Anderson of South Africa.