The Greeks sealed qualification beyond the group stage for the first time in their history on Tuesday, Georgios Samaras' stoppage-time penalty securing a 2-1 win over Ivory Coast.
That victory saw Santos' men finish second in Group C behind Colombia, earning them a last-16 match against surprise package Costa Rica in Recife on Sunday.
Coming into the finals, the Central Americans were given little chance by many to progress from Group D, having been drawn with Italy, Uruguay and England.
However, Jorge Luis Pinto's side defeated both Italy and Uruguay, before a 0-0 draw with England assured their position as group winners.
Although he enjoyed the historic victory against Ivory Coast, Santos was quick to turn his attentions to the next task at hand.
"We have already started to study the next game against Costa Rica," he said.
"Because if we want to continue writing history we should play as we played in the last two games.
"Costa Rica is a very strong opponent; everybody knows that.
"We are experiencing a very important moment in time and we must be very careful."
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