Udinese or Napoli can go above Lazio into the Champions League qualifying round berth if one of them wins their meeting in Udine later on Sunday (1945 GMT).
Former Juventus defender Nicola Legrottaglie grabbed Catania's winner following a corner 11 minutes from time to shoot Vincenzo Montella's flying Sicilians up to joint-sixth.
Lazio's defeat also meant leaders AC Milan and second-placed Juventus, who won 2-0 at Parma and 5-0 at Fiorentina respectively on Saturday, have a comfortable cushion over the Romans with 10 games left.
Milan are top with 60 points from 28 games followed by Juve on 56 and Lazio with 48. Napoli and Udinese both have 46 points ahead of AS Roma, who host Genoa, Inter and Catania all on 41.
Inter, dumped out of the Champions League by Olympique Marseille in midweek, have little hope of making next season's competition after Diego Milito missed a first-half penalty to leave Claudio Ranieri's side seven points behind Lazio.
Mauricio Pinilla got a hat trick as Cagliari coach Massimo Ficcadenti — reappointed last weekend four months after being sacked - returned for a 3-0 win over the nine men of ex-club Cesena, who are rock bottom and 14 points from the safety zone.
Second-bottom Novara won 2-0 at Siena to boost their outside chances of avoiding the drop and Lecce, in the third and final relegation spot, drew 1-1 at home to Palermo to stand five points adrift of Parma who are 17th in the 20-team standings.
Chievo drew 2-2 at fellow mid-table side Bologna.
