The Vatreni kicked off their campaign with a 3-1 loss against Brazil, but having thrashed Cameroon 4-0 last time out, Group A will now go right down to the wire in a shootout between the hosts, Croatia and Mexico.
"We had already played a good match against Brazil, but now we've shown how strong we are," Olic is quoted as saying by FIFA.com.
"We need to win again, and I believe that we can. We watched the Mexico game yesterday and we know that we are good enough to beat them and to qualify for the next round."
Olic became Croatia's oldest scorer at a World Cup finals by finding the net in his side's victory against Cameroon.