The 26-year-old, winner of 11 singles titles on the WTA Tour, was humbled 1-6, 2-6 by the Russian ranked 50 places below her, at Moscow's Olympic Sports Complex.

In beating Plíšková, Zvonareva, once the world number two, claimed her first win against a top 10 player since 2011 in this WTA Premier Tournament.

The result might have had significant consequences for Plíšková, who before the contest had not yet sealed her place at the season-ending tournament for the world's best players, the WTA Finals.

In the end, however, another shock result in Moscow today means Plíšková will play at the tournament in Singapore, due to take place between October 21 and 28, despite her defeat today.

That is because one of her rivals for a sport at the Finals, Kiki Bertens from The Netherlands, was also on the wrong end of an upset today.

She was sent on her way by Aliaksandra Sasnovich from Belarus, who stunned the number four seed and world number 10 6-3, 4-6, 6-3.

The 26-year-old Bertens had entered the contest knowing she had to make at least the semi-finals in Moscow to have a chance of qualifying for the final event of the season.

Today's defeat however, means Plíšková and Ukraine's Elina Svitolina take the final two available spots instead. 

In the quarter-finals Sasnovich is set to play either Britain’s Johanna Konta or Australia’s Daris Gavrilova,

In a third shock today, the 2017 US Open champion and world number eight Sloane Stephens, was knocked out by Tunisian qualifier Ons Jabeur.

Stephens, the number three seed in the tournament, was playing her first match at this event having been given a bye in round one.

Despite being fresher than her opponent however, she still did not get the start she was hoping for, losing comfortably 3-6, 2-6.

As a reward for her win, 24-year-old Jabeur is now scheduled to face Estonia’s Anett Kontaveit in the quarter-finals, who beat France's Kristina Mladenovic in her second round tie 6-2, 7-6.