Samuel Eto'o tapped Inter ahead on the rebound in the 14th minute after Lazio keeper Fernando Muslera had palmed out a header by the Cameroonian.
Lowly Lazio rallied in sub-zero temperatures at the San Siro but, apart from an appeal for handball against Maicon in the area, they created few clear chances for all their possession.
Third-placed Juventus, who have 30 points, were sunk by substitute Mariano Izco's late goal after Bosnian midfielder Hasan Salihamidzic had cancelled out Jorge Martinez's 23rd-minute spot kick for Catania.
FERRARA PRESSURE
"Our ship is in the middle of a storm and the only way out is staying united," Ferrara was quoted as saying by La Gazzetta dello Sport's website.
"The thought of quitting has not crossed my mind. If there were just one problem we'd have probably solved it.
"There are a series of things that aren't right. We know we haven't done as well in the last three months as at the start of the season but the solution is not in the transfer market," added Ferrara.
Club president Jean Claude Blanc said the former Italy and Juve defender's job was safe. "We have confidence in Ciro and his staff," said Blanc.
Sunday's matches between Genoa and Bari, and Udinese and Cagliari were hit by the weather along with Bologna's home game with Atalanta.
