The two teams meet in the first leg of their playoff on Friday night in Athens and Papastathopoulos, who represented his nation at the 2010 tournament, is desperate to help them reach the finals in Brazil next summer.
"We always play to win," he told UEFA.com. "It would be ideal to keep a clean sheet on Friday at home. We will see how these encounters unfold. They will be very tough, like finals.
"There is no tomorrow after Tuesday. Either we qualify and everything is perfect, or we get eliminated and everything is a mess. There is no other way to look at it. However, we hope to end up on the winning side."
Greece finished level on points in their qualifying group with Bosnia-Herzegovina, but missed out on an automatic spot for next summer's tournament due to their inferior goal difference.