Maria Sakkari, Jelena Ostapenko and Petra Kvitova all avoided upsets as the seeds continued to march on at the St Petersburg Ladies Trophy on Tuesday.
Top seed Sakkari beat Anastasia Potapova 6-4 6-4 to advance to the last 16, while seventh seed Ostapenko was a 6-1 6-4 winner against wildcard Wang Xinyu.
Kvitova, the 2018 champion, took just an hour and nine minutes to see off qualifier Jule Niemeier 6-2 6-1, with the sixth seed and two-time former Wimbledon winner making a positive first appearance since being eliminated from the Australian Open in round one.
Sakkari, Ostapenko and Kvitova followed fellow seeds Anett Kontaveit, Belinda Bencic and Elise Mertens – winners on Monday – in avoiding an early exit.
However, number four seed and home favourite Anastasia Pavlyuchenkova was forced to withdraw from the competition on Tuesday due to a knee problem.
Bernarda Pera replaced the Russian in the main draw and fell 7-6 (7-3) 6-4 to Jaqueline Cristian, who will next face Aliaksandra Sasnovich.
That is after Sasnovich held firm to beat Magda Linette 7-5 4-6 6-4 in a tight contest, with a decisive break in the fifth game of the third set seeing her through.