Vinci eased past Timea Babos 6-2 6-1 in her first round match on Wednesday but the Italian came unstuck in equally-easy fashion, losing 6-1 6-1 to Krunic, who now faces Polona Hercog in the quarter-finals.
Another result that raised eyebrows saw the exit of number four seed Julia Goerges as Danka Kovinic triumphed 6-4 6-7 (6/8) 6-2.
Romanian Monica Niculescu also made it through to the quarter-finals.
The number three seed dropped just five games as she defeated Teliana Pereira of Brazil in straight sets, 6-2 6-3.
Niculescu was joined in the last eight by compatriot Andreea Mitu as she edged an all-Romanian tie against Sorana Cirstea, coming from behind to win in three sets 5-7 6-2 6-4.
Finally, Slovakian seventh seed Anna Karolina Schmiedlova beat Denisa Allertova of the Czech Republic 6-1 6-2.