Angelique Kerber was the biggest casualty at the WTA Western and Southern Open on Wednesday as defending champion Karolina Pliskova reached the round of 16.

German third seed and former world number one Kerber was bundled out after Ekaterina Makarova converted her eighth match point in Cincinnati.

World number one Pliskova booked her spot in the last 16 with a routine victory over Natalia Vikhlyantseva.

Grand slam winner Petra Kvitova suffered another defeat to Sloane Stephens as the 14th seed departed the WTA Premier tournament, while American veteran Venus Williams also said goodbye.

KERBER UPSET IN CINCINNATI

It was a marathon but Kerber could not go distance, beaten 6-4 1-6 7-6 (13-11).

Makarova needed an eighth match point to close out the contest against the 2016 runner-up.

The win was Makarova's second of the year over Kerber – who did not look happy post-match after the Russian called the trainer multiple times throughout – having triumphed at the French Open.

STEPHENS TOPPLES KVITOVA

Makarova will go head-to-head with Stephens in the last 16 after the American dispatched two-time Wimbledon champion 6-2 6-3.

For the second time in as many weeks, Stephens got the better of Kvitova, having beaten the Czech in Toronto en route to the semi-finals.

Stephens needed just 70 minutes to progress.

PLISKOVA OFF TO WINNING START

Back to defend her crown, Pliskova was a comprehensive 6-2 6-3 winner.

Pliskova's success in Cincinnati a year ago inspired her run to the 2016 US Open final, while she was a quarter-finalist at last week's Rogers Cup.

She broke in each set to secure a clash with Italian Camila Giorgi, who overcame Dario Gavrilova 7-6 (7-1) 5-7 6-3. 

VENUS STUNNED BY BARTY

Enjoying a breakthrough year in 2017, claiming her first WTA Tour title, Barty upstaged Williams 6-3 2-6 6-2.

Australian qualifier Barty had previously lost all six matches against top-10 opponents but that changed thanks to her victory over the ninth seed.

Caroline Wozniacki, Madison Keys and Elina Svitolina were among those to win through.