Elena Rybakina ended Zheng Qinwen's spirited US Open run on Wednesday, guaranteeing her rise to world No. 1 as she booked a semi-final showdown with Coco Gauff.

Rybakina beat Zheng 3-6, 6-1, 6-4 and is assured of ending Aryna Sabalenka's reign atop the standings -- even if the Belarusian wins a third straight title.

"It's just a number right now," Rybakina said. "It's a different achievement ... but mostly you think about the titles in the end of the day."

Therefore the 27-year-old Kazakh star will be focused on Gauff, who saved two match points in a 2-6, 7-6 (9/7), 6-2 victory over Russian 19-year-old Mirra Andreeva, the fifth-ranked reigning French Open champion from Russia.

Sabalenka will play third-seeded Jessica Pegula in Thursday night's semi-finals -- the first time since 1975 at the US Open that the top four women all made it to the penultimate round.

Top-seeded Alexander Zverev completed the men's semi-final lineup, cruising past Botic van de Zandschulp 6-2, 7-5, 6-1.

Gauff made it by the skin of her teeth, struggling early and saving two match points in the tiebreaker.

She rallied with some inspiration from Frances Tiafoe's come-from-behind five-set victory over Alex Michelsen.

"I just had to reset," Gauff said. "Honestly, I was thinking about Frances Tiafoe and how he came back. I was just trying to leave the court without regrets."

Rybakina, the first Kazakh player to reach number one, is chasing a third Grand Slam title after winning the Australian Open in January -- four years after winning Wimbledon.

"I feel like you will appreciate and think about it even more when you finish your career," she said of the ranking. "Like now, you still need to keep on going."

Reigning Olympic champion Zheng, a former world number four ranked 121 after missing about eight months due to elbow surgery, went through qualifying and won seven matches in New York, including comeback wins over six-time Grand Slam champion Iga Swiatek and former Australian Open winner Madison Keys

She rocked Rybakina early behind fierce serve and a variety of shots, effectively neutralizing the Kazakh's power until a slight dip allowed Rybakina to seize control in the second set.

In a close third Zheng missed a chance to break in the third game. Rybakina broke her in the next and rocketed to victory.

"I got lot of chances in the third set, but I didn't took it," Zheng said. "That was a bit pity for me to lose this match, but obviously I could take positive things from US Open this year."

- Zverev rolls through  -

Zverev was largely untroubled against Dutch veteran van de Zandschulp, who upset Carlos Alcaraz in the second round two years ago and beat sixth-seeded Australian Alex de Minaur in the second round last week.

The reigning French Open champion won the last five games of the opening set to go one set up after just 37 minutes, and saved a set point in the penultimate game of the second before breaking van de Zandschulp to pocket the set.

He ran away with it in the third to give himself another early night in a tournament that saw him labor into the early hours of the morning in first- and second-round five-setters.

Zverev will face veteran Karen Khachanov for a place in Sunday's final.

Khachanov advanced when Belgian Alexander Blockx retired from their quarter-final with the Russian leading 6-2, 7-5, 3-2.

"I saw really that he was suffering all over his body," Khachanov said of 21-year-old Blockx, who had already been on the verge of retiring from his fourth-round win over Francisco Cerundolo with a rib injury.

On Wednesday he played with one thigh wrapped and had medical timeouts for treatment on one foot and pain in his lower back that hindered him much of the match. 

"I think today my body just gave up," Blockx said. "I think I finally understand how physical the slams are."