Karolina Pliskova lost a first-round match for the first time in 2017 as she was dumped out of the Prague Open 7-6 (8-6) 6-2 by Camila Giorgi.
World number three Pliskova had made at least the quarter-finals of this tournament in her last three appearances, including a title-winning success in 2015.
Giorgi had lost her last seven matches against top-10 ranked opposition, but a tenacious performance helped her to victory this time around, the Italian saving four of the five break points that Pliskova carved out.
And the Czech's struggles on second serve, winning just 46 per cent of points, played further into Giorgi's hands.
There was more to shout about for the home fans as 17-year-old wildcard Marketa Vondrousova beat Carina Witthoeft 6-7 (6-8) 7-5 6-2.
Oceane Dodin and Wang Qiang also reached the second round after victories over Annika Beck and Maria Sakkari respectively.