Coco Gauff reacts to the crowd after winning her quarterfinal...

Coco Gauff reacts to the crowd after winning her quarterfinal match against Jelena Ostapenko at the U.S. Open on Tuesday. Credit: Kathleen Malone-Van Dyke

 Karolina Muchova and Aryna Sabalenka are well aware of what they will face at Arthur Ashe Stadium in Thursday night’s U.S. Open women’s semifinals.

To put it bluntly: a thorough lack of support when they encounter a pair of popular Americans in Coco Gauff and Madison Keys.

“We are realizing that the crowd will be not probably on our side,” Jaroslav Blazek, one of Muchova’s coaches, said on Wednesday.

“And we know how Coco is playing right now. She’s in good shape and the results showed us that right now she’s in a very good mood.”

All true, as Gauff, 19, has become the darling of Open crowds in becoming the first American teenager — man or woman — to reach an Open semifinal since Serena Williams in 2001.

And Gauff did beat Muchova, 6-3, 6-4, on Aug. 20 in the final of the Western & Southern Open in Cincinnati.

“But honestly,” Blazek said, “we are thinking like Karolina is playing better than two weeks before, compared with her performance in the (Cincinnati) final.

Karolina Muchova returns a shot to Sorana Cirstea during the quarterfinals of...

Karolina Muchova returns a shot to Sorana Cirstea during the quarterfinals of the U.S. Open. Credit: AP/Charles Krupa

“So we believe it will be enough. There is a big chance and we are expecting a big fight, there is no doubt.”

Gauff is the No. 6 seed and Muchova No. 10. The other semifinal will feature Keys, the 17th seed, against No. 2 seed and soon-to-be world No. 1 Sabalenka.

Keys won her quarterfinal Wednesday night over Wimbledon champion Marketa Vondrousova, the No. 9 seed, 6-1, 6-4. “I love playing here,” Keys said on the court afterward. “In front of a home crowd you never feel like you can’t get out of any situation.”

Sabalenka advanced earlier in the day by dismissing No. 23 seed Qinwen Zheng, 6-1, 6-4. She was unsure who her semifinal opponent would be when she spoke to reporters, but she knew what to expect if it was Keys.

“I understand, of course, they will support her more than me,” she said. “I had this experience playing on the stadiums where people were supporting my opponents. So it’s not going to bother me anyhow. I mean, I’ll just try to stay focused and try to play my best tennis.

“I know that I have my team in the box. I have my friends in the stadium who are cheering for me. I have my family, and it’s enough for me.”

Sabalenka, who won the Australian Open this year, has reached at least the semifinals of all four grand slam tournaments. She has not lost a set in the Open.

Finishing Zheng off in a mere 1:13 was a bonus given the extreme heat and the fact there will be no day off before the semifinals for Sabalenka.

She grew up in chilly Belarus but now lives and trains in south Florida, which she said helped prepare her for the conditions.

“I mean, it was hot, but yeah, because I did my preparation in Florida, I mean, what can be worse than Florida?” she said. “I mean in July and June. Not overall.

“So yeah, I think that’s really helped me today to stay strong and not really get tired because of the heat.”

Keys moved to Florida when she was 10. Gauff grew up in Florida. That could be an edge against Muchova, a Czech who seemed to struggle in the heat of Cincinnati. (Gauff and Jessica Pegula lost to Su-Wei Hsieh and Xinyu Wang in the doubles quarterfinals, 7-6, 3-6, 6-4, on Wednesday.)

The heat wave was a story all day, with the men’s No. 3 seed Daniil Medvedev saying this after winning in three sets in his quarterfinal against Andrey Rublev, “Let’s call it dangerous.”

The good news is that both women’s semifinals will be played at night.

Blazek said of Muchova, “We are sure that she will fight like a lion.”

Perhaps, but she will be a lion in Gauff’s den.