Inter coach Roberto Mancini was sent off for sarcastically applauding the referee, then Marco Materazzi went for a lunge on Goran Pandev. Julio Cruz thumped Aleksander Kolarov - which left the Lazio defender with a bleeding ear - was not spotted by the officials before he scored.
"These things happen and there can be tension on the field, but the important thing is to show fair play and that's what we did tonight."
Cristian Chivu and Nicolas Andre Burdisso went off the pitch with a shoulder and back injury respectively.
Chivu seemed to come off worst and made a gesture on his way out that this was a serious problem.
"I hope the injuries aren't too serious, as it would be a shame at this stage," added Zanetti. "Now we have to prepare for the game with Siena, which means a great deal to us and all the Inter fans."