Jorge Pinto's men showed they aren't the whipping boys everyone expected as they overturned a one goal deficit to pick up all three points from their opening game
An Edinson Cavani penalty opened the scoring in the first half before two quickfire goals from Joel Campbell and Oscar Duarte reversed the scoreline. Marco Urena's delightful finish secured the three points with five minutes left on the clock.
With Italy and England completing a strong-looking Group D, Costa Rica was expected to be the whipping boy even with star striker Luis Suarez - still recovering from a knee injury - unable to take the field in Fortaleza on Saturday.
However, the two-time world champions were left stunned as their opponents counterattacked with purpose and scored three second-half goals to spring a major surprise.
A stunned Uruguay was unable to avoid a loss that leaves its hopes of progression looking bleak. An injury-time red card for Maxi Pereira only served to compound the misery.
There were plenty of early warning signs as Uruguay struggled to break down its opponent's 4-5-1 formation.
Uruguay's annoyance grew stronger soon after, too, as the usually reliable Cavani missed a golden opportunity when volleying wide from a deflected Diego Forlan free kick.
Costa Rica's failure to heed that warning proved costly as Junior Diaz hauled down Diego Lugano in the box from an identical Forlan set piece.
Cavani made no mistake this time as he arrowed a penalty beyond the dive of Keylor Navas.
Yet Jorge Luis Pinto's side found a response, showing it had the attacking capabilities to match its defensive nous in a promising spell highlighted by Campbell firing narrowly wide with a fizzing strike from distance.
The underdogs were soon indebted to a stunning save from Navas, though, as he turned Forlan's deflected effort over just before halftime.
It was Navas' opposite number Fernando Muslera who had to be alert immediately after the break, keeping out Duarte's header from point-blank range.
He could do little moments later, however, as Campbell fired home a half-volley after fine work from Cristian Gamboa.
Things soon went from bad to worse for Uruguay. Duarte stole in at the back post, albeit with a suspicion of offside, to head home another fine Gamboa delivery.
Dangerous pot-shots from Campbell and Bryan Ruiz threatened further damage, yet there was soon a warning flash at the other end as Cavani forced a good reactionary stop from Navas.
Hopes of a Uruguay comeback were ultimately extinguished with six minutes remaining as Campbell's wonderful through ball freed Urena, who belied the tight angle by superbly sliding beyond the onrushing Muslera.
If that goal added further gloss for Costa Rica, the game's last flashpoint summed up Uruguay's evening as Pereira was sent off for a wild hack at the impressive Campbell.