Cambiasso tapped in from an offside position and moments later David Suazo completed the 2-0 win.
"If it was indeed offside, then it was very difficult to see. The referee officiated well throughout," insisted Inter coach Roberto Mancini afterwards.
"The first half was balanced and Catania did very little to score. We improved after the break and were repaid for taking the risk of introducing a third striker. It was important to win here and not give our opponents too many chances."
Catania coach Silvio Baldini tried to calm the atmosphere by defending the official.
"These mistakes can happen and we have to accept them, otherwise there will be controversy every single week," he warned.
"I can accept this error frankly today, although I know my President and the Catania fans will go home less than happy tonight. What I do ask is equality - we have to retake a free kick, but if a big club does the same thing it is allowed.
"We knew that we could not afford a single mistake and with anything Inter would have taken the lead, making it an uphill struggle. We had to play the way we did, trying not to run risks, but unfortunately the goal came out of nowhere."