Francesco Lodi hit the early penalty which earned Catania a 1-0 Serie A victory against a Siena side whose problems go from bad to worse.
Siena coach Giuseppe Sannino had called for an immediate response from his players after their 4-1 defeat at Lecce on Sunday.
But, despite pouring pressure on the Catania goal in the closing 20 minutes, there was little sign of the message Sannino had wanted his players to send out.
They sit uncomfortably two points above the relegation zone, while Catania are now nine points clear of the bottom three, comfortably in mid-table in 10th position.
The game at the Artemio Franchi stadium was originally due to be played earlier this month, but was postponed due to heavy snow in Siena.