The WTA Western and Southern Open semi-finals are set after defending champion Karolina Pliskova, Garbine Muguruza, Simona Halep and Sloane Stephens advanced to the final four.

World number one Pliskova played twice on Friday, against Camila Giorgi and Caroline Wozniacki, as she booked her spot in the Cincinnati semis.

She earned a final-four showdown with Wimbledon champion Muguruza, who outlasted fellow seed Svetlana Kuznetsova in three sets.

The other semi will be contested by second seed Halep and Stephens at the WTA Premier tournament on Saturday.

PLISKOVA SURVIVES LONG DAY

The Czech star had to back up in consecutive games on Friday.

After rain washed out play on Thursday, Pliskova resumed her last-16 clash with Giorgi and triumphed 6-3 4-6 6-0.

Pliskova then produced a dominant performance to see off former world number one Wozniacki 6-2 6-4.

Just 66 minutes were needed as Pliskova avenged her loss to Wozniacki at the Rogers Cup last week.

MUGURUZA WINS MARATHON

After saving three match points against Madison Keys a day earlier, it did not get easier for Muguruza.

The Spanish fourth seed – who hit 34 winners and tallied 47 unforced errors – edged Kuznetsova 6-2 5-7 7-5 in two hours, 45 minutes.

Muguruza appeared set for a routine win when she led 6-2 3-1 in the second set but the Russian eighth seed – with 40 winners of her own – rallied in a thrilling encounter.

"I think it was probably one of the best matches of the year, you know, because I felt like we both played very well. Especially in that third set, you know, we were winning points and our serve was there," Muguruza said. "I know that I won, but I'm sure she feels it was a great match, as well, because a tough battle and very hot out there."

HALEP INTO ANOTHER CINCINNATI SEMI

For the third consecutive year, Halep will contest a semi-final at the Western and Southern Open.

The Romanian was too good for seventh seed Johana Konta, winning 6-4 7-6 (7-1).

It was another case of revenge as 2015 runner-up Halep bounced back from her loss to Konta at Wimbledon.

STEPHENS GOES BACK-TO-BACK

It was also a jampacked day for Stephens, who topped Julia Goerges 6-1 7-6 (7-3).

Resurgent American Stephens – who has recovered from a severe foot injury – survived a three-set match with Ekaterina Makarova 2-6 6-3 6-4.

And Stephens backed that up to reach a second successive Premier semi-final, having made it through to the final four in Toronto last week.