Not taking away any accomplishments of other teams but Costa Rica is definitely the surprise team in this tournament. Costa Rica was given no chance whatsoever and left three former World Cup Champions (Italy, England and Uruguay) behind them. They are entering the knockout for only the second time. The first time in 1990 they lost to Czechoslovakia (a country which does not exist anymore) 4-1 in the final 16.
With a win they would continue their Cinderella tournament and face the Netherlands.
Chances for Costa Rica are good as they are facing a team which has trouble scoring. Only 12 goals in 10 qualifying games facing teams like Latvia, Lichtenstein and Slovakia and only 2 goals in 3 group matches. Both goals were scored in the last game. Greece's success is definitely based on defense (4 goals against in 10 qualifying games) .
Costa Rica should continue their success. If they take a page out of the Colombian play book and score early and force Greece to go more offense they will blow Greece out. The longer the game goes on and Greece stays in it the higher the chances are of a low scoring game or even a Greece upset.
I think Costa Rica will score early and plenty. 3-0. The dream continues.