The result leaves Inter, which has one win from six games, languishing just outside the relegation zone, while Catania moved into sixth ahead of the weekend's remaining games.
Esteban Cambiasso gave Inter the perfect start when he volleyed in Maicon's cross after six minutes. That seemed to spark Catania into life but it could not find a way past a solid Inter defense.
The match was turned on its head in five second-half minutes. Catania got back on level terms almost immediately after the restart when Gonzalo Bergessio raced from just inside his own half and slotted the ball to Sergio Almiron, who lifted it over Inter goalkeeper Luca Castellazzi from the edge of the area.
Things went from bad to worse for Inter in the 50th minute when Castellazzi was adjudged to have brought down Bergessio and Francesco Lodi fired home the resulting penalty to give Catania the lead.
Inter tried to find a way back into the game but without success and it was Catania who went closest to scoring when, in the 82nd minute, Andrea Catellani raced clear on the counterattack, but Castellazzi got down well to divert the danger.
Cambiasso almost rescued a point for Inter in injury time, but the ball was scrambled clear by the Inter defense as the Argentina midfielder was about to strike.
