Svetlana Kuznetsova was among three seeds to bow out of the Prague Open on the competition's opening day as she was beaten 6-4 6-3 by Zhang Shuai
Camelia-Irina Begu and Camila Giorgi were also beaten on the clay in the Czech capital although Kuznetsova's defeat was perhaps the most surprising.
The world number 27 had won each of her previous four meetings against Zhang but came unstuck on Monday - despite the Chinese wasting four match points before sealing her progress.
Katerina Siniakova also caused an early upset with a 6-3 6-3 victory over sixth seed Romanian Begu.
The world number 76 failed to save either of her break-point opportunities but still had enough to sweep aside the sixth seed in their third meeting of 2015.
The seeded entrants continued to exit throughout the day, as Giorgi tasted defeat in a close-fought 4-6 6-3 7-5 reversal to Yanina Wickmayer.
The Italian had threatened to claim victory when she fought back from 4-1 down to level at 5-5 in the final set.
However, Wickmayer secured the final two games with the help of her seventh break of serve - ensuring a second-round meeting with Aleksandra Krunic.
There were no such worries for fifth seed Alize Cornet who made a winning start to her clay court season - easing past wildcard Kristina Schmiedlova 6-3 6-3.
Fresh from a run to the Katowice Open quarter-finals, Cornet surged into a 4-0 lead and was rarely troubled from thereon in.
British number one Heather Watson was beaten 7-5 3-6 7-6 (7-5) by Slovenia's Polona Hercog in an epic encounter that lasted more than three hours.
Hercog will face Siniakova in the second round while home favourite and wildcard Denisa Allertova sprung a surprise against America's Coco Vandeweghe - making the most of six double-faults to progress 6-4 6-1.
There were also wins for Krunic and Elena Vesnina over Mirjana Lucic-Baroni and Jana Cepelova respectively.