Marosi, a crowd favorite at the Romai Tennis Academy in Budapest, defeated the Bulgarian player 6-2, 7-6 (7-2) to reach the quarterfinals of the clay-court event.
Seventh-seeded Klara Zakopalova of the Czech Republic also advanced, crushing Mathilde Johansson of France 6-0, 6-1.
Others moving on to the quarterfinals were Czech Petra Kvitova, a 6-2, 6-2 winner over Martina Muller of Germany, and Hungary's Greta Arn, who eliminated Slovakian qualifier Zuzana Kucova 6-2, 6-1.
All quarterfinal matches are scheduled Friday. Second-seeded Alize Cornet of France meets Anna-Lena Groenefeld of Germany, Slovenian Andreja Klepac goes against Kvitova, Marosi takes on Croatia's Karolina Sprem and Zakopalova plays Arn