The 26-year-old was serving for the match at 5-2 in the second set when the heavens opened Friday evening.
Svitolina would be Wang's highest-ranked top ten scalp this year.
She was unable to capitalise on her stay of execution despite breaking Wang to go 3-5 and then holding her own serve.
"I had nothing to lose against her - she's a very good player", Wang said of Muguruza.
"But in the end (Wang) had the advantage, she had the confidence", Svitolina said.
"It was (the) toughest game", she said.
It is likely that Ukrainian tennis player Elina Svitolina will become a party to the last tournament of the worldwide tennis Association in this season, the Kremlin Cup.
Dayana just 1 hour and 6 minutes, defeated Wang Qiang and became the youngest champion of the WTA tournament in the history of Ukraine.
Svitolina, one of five players chasing the last three spots at the BNP Paribas WTA Finals Singapore, hadn't dropped a set in two matches heading into the quarterfinal. She reached the fifth semifinal in 20 tournaments played in her 2018 campaign full of ups and downs that brought her to seal the sixth career title in Monterrey coming back from a set down to defeat Timea Babos in the final. Her previous title came in 2015 at the Ricoh Open.
Zhang will be favourite to win against 18-year-old Yastremska, now ranked 102.
"I was getting myself into too much trouble leaving the balls hanging in the middle of the court", said the Australian.
"But if before the match you think it s going to be really hard you up your focus, and when you go on court you stay more dedicated to each point, that s what helped me to stay that calm during the whole match".
"I even started to cry a little bit".
Wang had grabbed headlines at the French Open with her straight sets demolition of Venus Williams, and overcame Karolina Pliskova in both Beijing and Wuhan.