Elmira almost struck first, but a first-period goal by Jean Bourbeau was waved off due to goalie interference.
Instead, Florida landed the first blow on a Scott Pitt second-period goal.
Bobby Raymond added to the Everblades' lead in the third frame, and goalie Pat Nagle preserved the win with a 24-save shutout.
Elmira and Florida play again Friday night in Estero. Another Jackals loss would signal the end of the season for the Eastern Conference's top seed.
If Elmira wins Friday, Game Six would be back in Elmira Monday night.
The Jackals rallied from a 2-0 series deficit in the first round to beat Reading in five games. They will need a similar performace to keep playing past Round Two.