Pliskova is the world No.2 but has never won a grand slam championship or any of the top Premier tournaments, with triumphs at the Cincinnati Masters and Italian Open — Premier 5 events — the highlights of her career.

The Czech star was unable to end her drought in the final Premier Mandatory competition of 2019, losing to Jelena Ostapenko in the last 64.

Ostapenko retired at the Tashkent Open with a gastrointestinal illness earlier this week and served up 25 double-faults here but still dictated the play against Pliskova.

The No.2 seed saved an incredible 18 break points yet let six slip through and Ostapenko emerged a 7-5 3-6 7-5 victor.

Ostapenko next plays Katerina Siniakova, who defeated Chinese wildcard Wang Xiyu in straight sets.

The draw would appear to have opened up for Simona Halep in the same quarter, but other seeds fared better than Pliskova in their own openers.

BERTENS, BENCIC THROUGH

Kiki Bertens might have joined Pliskova in an early exit but she recovered impressively from a set down to beat the dangerous Donna Vekic in three.

The Dutch star dominated the second set as Vekic threatened to collapse and, although the Croatian recovered, victory was sealed with a tie-break, 3-6 6-1 7-6 (7-3).

US Open semi-finalist Belinda Bencic found life a little easier as she downed Hsieh Su-Wei 7-5 6-2.

She explained: "I thought I had to be really aggressive today and not play too many rallies because she's the best in those.

"Normally my game is more medium aggressive, but today I was more so. I think it worked out well."

KENIN SERVES UP A BAGEL FOR MUGURUZA

Garbine Muguruza, champion here in 2015, could not complete what would have been a remarkable comeback against Sofia Kenin.

Kenin took the first set 6-0 but two-time grand slam winner Muguruza battled back to win the next 6-2 and was a break up in the decider before losing it 6-2.

Daria Kasatkina did produce a turnaround in her 2-6 6-4 6-4 victory over Peng Shuai, while Zheng Saisai saw off Monica Puig and Polona Hercog edged past Julia Goerges.