New York — All eyes at the U.S. Open will turn to the women’s tennis semifinals Thursday night — and the shadows created by the partially closed retractable roof at Arthur Ashe Stadium.

Under a new rule adopted on Tuesday for the rest of the event, the U.S. Tennis Association partially closed the retractable Ashe roof — normally used to block out rain — to provide some additional protection from the sun for spectators and competitors.

One unintended result: The shadows can make it hard to see the tennis balls as they zip through the air.

Watch: Coco Gauff’s Quarterfinal Highlights

Zheng Qinwen, the No. 23 seed who defeated 2022 runner-up Ons Jabeur in her previous match, said that dynamic bothered her during a 6-1, 6-4 loss to Aryna Sabalenka.

Sabalenka won 20 of the initial 24 points to race to a 5-0 lead after just 17 minutes.

She reached the semifinals for the fifth major in a row and will rise from No. 2 to No. 1 in the WTA rankings next week, replacing 2022 U.S. Open champion Iga Swiatek, who exited in the fourth round.

As for the hot weather? Sabalenka, a 25-year-old from Belarus, said her training base in the United States prepared her well for the heat and humidity, which rose above 50%.

“I mean, it was hot, but because I did my preparation in Florida — I mean, what can be worse than Florida? I mean, in July and June, you know. Not, like, overall,” said Sabalenka, who has dropped a total of just 21 games through five matches over the past 1 1/2 weeks. “So I think that’s really (helping) me today to stay strong and (not) really get tired because of the heat.”

She improved to 7-0 in major quarterfinals as she seeks her second Slam trophy to go alongside the one she won at the Australian Open in January.

Sabalenka will meet 2017 U.S. Open finalist Madison Keys, an American who saved all nine break points she faced during a 6-1, 6-4 victory over reigning Wimbledon champion Marketa Vondrousova. The other women’s semifinal will be No. 6 Coco Gauff against No. 10 Karolina Muchova; they won their quarterfinals on Tuesday.

“It’s going to be a lot of hard hitting, not a lot of long points,” said Keys, who lost to Sabalenka at Wimbledon in July. “Just going to try to buckle up and get as many balls back as I can.”

Keys vs. Vondrousova was interrupted for eight minutes at deuce in the first game, when a spectator in the lower level needed medical attention. Keys brought two towels and a bottle of water over to where the fan was being helped. The U.S. Tennis Association said the episode was not heat-related.

Watch: Madison Keys Quarterfinal Highlights

Men’s Semifinals Are Friday

Daniil Medvedev will get back on court on Friday for his semifinal against defending champion Carlos Alcaraz, a 6-3, 6-2, 6-4 winner over 2020 U.S. Open runner-up Alexander Zverev on Wednesday night. Alcaraz saved all five break points he faced and converted all four he earned on Zverev’s serve.

The other men’s semifinal is 23-time major champ Novak Djokovic vs. unseeded Ben Shelton.

Medvedev wore a white towel around his neck during the on-court interview at Arthur Ashe Stadium after finishing off the 2-hour, 48-minute match, which is relatively short for a best-of-five-set Grand Slam men’s match.

Medvedev said he felt dizzy afterward and that both he and Rublev rubbed their faces raw by toweling off so frequently. Rublev described feeling his heart racing between points.

Asked about his level of concern on a day like that, Rublev said: “I’m not even thinking about my health.”