Top seed Karolina Pliskova was an opening-day casualty at the J&T Banka Prague Open as the unseeded Camila Giorgi caused a surprise.
The Italian eventually converted her sixth set point in a first-set tie-break before winning games on Pliskova's serve twice in the second to secure a 7-6 (8/6) 6-2 success.
Pliskova, ranked third in the world, was beaten by an opponent 99th in the standings, and Giorgi said on wtatennis.com: "This is the biggest achievement in my career, beating a top-three player.
"I am happy but not too happy, because I always thought I could win against top-10 players."
Wild card Marketa Vondrousova also progressed, as did Oceane Dodin and Wang Qiang.
Fourth seed Timea Babos suffered a first-round exit at the Grand Prix De SAR La Princesse Lalla Meryem as Francesca Schiavone once again showed her clay-court form.
The 2010 French Open champion is a wild card entry in Morocco but she remains undefeated on clay this term having won a sixth contest on that surface by beating Babos 6-4 6-1.
Schiavone's Italian compatriot Sara Errani defeated Anna Blinkova 6-3 6-3, while Ekaterina Makarova, Varvara Lepchenko and Yulia Putintseva were also victorious.
