Spain's Suarez Navarro brushed aside Hungarian Timea Babos 6-2, 6-2 on the outdoor hard courts in Florianopolis, joining fifth-seeded Niculescu in the second round.
The Romanian champ, who topped Russian Olga Puchkova in last year's final, moved on with a 6-0, 4-6, 6-2 decision over Slovakian Anna Schmiedlova.
Also Monday, second-seeded Spaniard Garbine Muguruza downed American Vania King 6-2, 3-6, 7-5, but No. 4 seed Francesca Schiavone fell victim to Czech Barbora Zahlavova Strycova in a 6-4, 1-6, 7-5 upset.
Romanian No. 6 seed Alexandra Cadantu topped Brazilian wild card Gabriela Ce 6-1, 6-3, while No. 8 Paula Ormaechea of Argentina breezed past Brazilian wild card Beatriz Haddad Maia 6-1, 6-2.
South African Chanelle Scheepers, Kazakhstan's Yaroslava Shvedova and Germany's Dinah Pfizenmaier also logged first-round wins.