Caroline Wozniacki's first appearance since the Australian Open ended in disappointment as she was dumped out of the St Petersburg Ladies Trophy by Dominika Cibulkova in round two.
Third seed Wozniacki suffered a disappointing first-round defeat to Yulia Putintseva in Melbourne last month and was looking to get her season back on track in Russia.
However, Wozniacki - handed a bye in round one - was sent packing by Cibulkova in a 6-4 7-5 defeat in a match that lasted two hours.
Cibulkova, who had not beaten Wozniacki since 2011, showed signs of nerves when wasting two match points in failing to see out the contest at 5-4.
She broke straight back, though, and Cibulkova did not miss her opportunity the second time round as she booked her place in the quarter-finals.
Top seed Belinda Bencic battled into the last eight despite the world number 11 struggling on serve in a 7-6 (7-3) 6-3 win over Annika Beck.
There were eight breaks of serve in a topsy-turvy first set, and Bencic once again failed to hold when serving for the match at 5-3 in the second.
However, Beck failed to make the most of the reprieve and Bencic broke straight back to ensure her progression.
Daria Kasatkina plays Cibulkova in the last eight after she defeated lucky loser Laura Siegemund 6-3 6-4.
Timea Babos saw off ninth seed Monica Niculescu in three sets and she next faces qualifier Kateryna Kozlova, who was also taken the distance in her win against wildcard Elena Vesnina.