"It's been long ride definitely. Everything came to my mind when I had my whole family, people who I loved to help me through the tough, tough time," said Kvitova. "I was just playing in the Philippe Chatrier, it was such nice to win the match and to be in the quarterfinal."
The last set became a lop-sided affair for Tianjin, which went on a 12-4 run to pull away and kept the advantage until the end.
Her former teammate in Beijing, Shi Xiufeng, showed an eagerness to return to court.
Next for Zhang is the winner between Czech No.7 seed Petra Kvitova and Canadian teenager Leylah Fernandez. Enditem
The visitors from Poprad did not put on an offensive show either, but scored twice, which was sufficient for earning their first victory of the season.
Swiatek is to face another unexpected winner from the fourth round - Martina Trevisan, as the world No. 159 stunned another title favorite Kiki Bertens 6-4, 6-4 in a later match on Court Suzanne-Lenglen.
Xinhua looks at some of the major talking points ahead of Thursday's opening day of fixtures in CONMEBOL's road to Qatar 2022.
"I think I played a really good match. I was very aggressive. I knew from last year I had to change something, so I really wanted to be better than last year and definitely, I was today," said the world No. 2.
Djokovic showed great sportsmanship in the match when rain fell down heavily on Galan's side of the court as the new Court Philippe-Chatrier roof was closing, the Colombian slipped over. Djokovic responded by calling a pause of the match until the conditions came back equal for both sides.
The game went into turmoil after that as Ciro Immobile was sent off in the 69th minute for slapping Arturo Vidal after being tripped by the Chilean, while Inter's midfielder Stefano Sensi also saw red in the dying minutes.
Schwartzman stunned Nadal 6-2, 7-5 two weeks ago in the Italian capital.