The WTA Western and Southern Open was halted because of rain, but Simona Halep and Garbine Muguruza managed to progress to the quarter-finals earlier in the day.

Wet conditions in Cincinnati forced the cancellation of play approaching midnight after second seed Halep and Muguruza already booked their spots in the last eight.

Halep was a winner in straight sets against Anastasija Sevastova, while fourth seed Muguruza fended off four match points in her victory over Madison Keys.

Former world number one Caroline Wozniacki also won through but defending champion Karolina Pliskova was halted by rain at the Premier tournament.

Pliskova was leading Camila Giorgi 3-0 in the first set when play was stopped, while Sloane Stephens, Ekaterina Makarova, Elina Svitolina and Julia Goerges were unable to take to the court.

HALEP MARCHES ON

The Romanian star is a woman on a mission after easing past Sevastova 6-4 6-3.

A runner-up in 2015 and semi-finalist last year, Halep advanced to the Cincinnati quarter-finals for a fifth successive year.

Halep was down 4-2 in the opening set but she rallied to win the next four games and never looked back.

"The match felt quite tough; it was not easy at all," Halep said. "I can say that I'm not playing my best tennis in this moment, but winning, even if I play less good, I think it's a big plus for me. It gives me a little bit more power, inside, that I can handle it."

Johanna Konta awaits in the quarters following her 6-3 6-4 win over Dominika Cibulkova.

MUGURUZA SURVIVES KEYS TEST

The Wimbledon champion was forced to dig deep, very deep against sixth seed Keys.

Following a lengthy rain delay in the final set, Muguruza trailed 4-2 and faced elimination at 6-5 and 40-15 before prevailing 6-4 3-6 7-6 (7-3).

Next up is eighth seed Svetlana Kuznetsova, who defeated Carla Suarez Navarro 6-4 6-2.

WOZNIACKI ENDS BARTY RUN

Barty took down Venus Williams but the Australian was stopped in her tracks by Wozniacki.

Wozniacki claimed a 6-4 6-2 victory as she progressed to the last eight of the tournament for the fourth time in her career but first since 2014.

The two-time US Open finalist will face either Pliskova or Giorgi on Friday.