The Greeks edged into the second round of the tournament thanks to a dramatic 2-1 win over Ivory Coast in their final match of Group C.
While admitting that Costa Rica will give Greece a "very tough game", Santos has confidence in his players to win the match and reach the quarter-finals.
"I expect it to be a very tough game," he told FIFA.com. "They've already shown they are a strong team, and team is the operative word.
"Collectively they are very effective, but we'll be ready for them. If we want to advance to the quarter-finals, and we do want to, we have to be better than them in key aspects of the game."
Greece had never made it through to the second round of a World Cup until this year.