Elena Rybakina needs just two wins to claim top spot in the WTA rankings heading into the US Open after Aryna Sabalenka's slump continued.

Sabalenka, who will be aiming for a three-peat at Flushing Meadows in the season's final grand slam, suffered a shock defeat to Sara Bejlek in the fourth round at the Cincinnati Open.

It means Rybakina, who swatted aside Diana Shnaider 6-4 6-4, is within touching distance of the world number one ranking. 

The Kazakh will take top spot away from Sabalenka should she reach the final in Cincinnati, though she has a tricky last-eight tie against Iga Swiatek - who she lost to last week in Toronto - to navigate.

Sabalenka was 5-1 up in a first-set tiebreak and 4-1 ahead in the second set, yet on both occasions the Belarusian failed to hold her nerve, with Bejlek rallying to clinch the biggest win of her career so far, prevailing 7-6 (9-7) 6-4.

"I totally lost my words. I just keep believing and that was the key today," said the 20-year-old, who won the Abu Dhabi hard court title in February as a qualifier," said Bejlek, who is into her first WTA-1000 level quarter-final, having claimed a maiden top-10 win.

"She played amazing tennis and I was just believing, keep fighting and I was just trying my best and that's it."

Next up for Bejlek is Madison Keys, who beat Wang Xiyu 7-6 (7-3) 6-4.

Amanda Anisimova and Jessica Pegula teed up an all-American showdown.

Anisimova beat Wimbledon champion Linda Noskova 6-1 6-4, while Pegula overcame Sorana Cirstea 6-4 4-6 7-5.

Coco Gauff got the better of Marie Bouzkova in straight sets, and the fourth seed will face Marta Kostyuk for a place in the last four.

1 - Sara Bejlek is the only quarter-finalist at this year’s Cincinnati Open to not have won a WTA-1000 event – since 2009, it is only the second time this has happened at the event after 2014 (Elina Svitolina). Parallel?#CincyTennis | @CincyTennis @WTA pic.twitter.com/t1caS7RYiD

— OptaAce (@OptaAce) August 20, 2026

Sabalenka's struggles roll on

Sabalenka won three tournaments before the end of March, but since her victory at the Miami Open, the 28-year-old has only reached one semi-final.

This is the first time a world number one has lost before the quarter-finals at three successive WTA Tour-level events since Naomi Osaka in 2019 (Dubai, Indian Wells, Miami).

But as gloomy as the outlook is at the moment for Sabalenka, who will be hoping for a big favour from Swiatek when the Pole faces Rybakina, the day belonged to Bejlek.

The 20-year-old is the only quarter-finalist at the Cincinnati Open to have not won a WTA 1000 tournament. It is only the second time this has happened at this event, after Elina Svitolina in 2014.

However, if she gets ahead, then Bejlek is difficult to stop.

She has won 17 of her 18 matches in which she has won the first set this season.