Hernan Crespo struck Inter's opener before Tommaso Rocchi levelled for the hosts and Rossi lamented afterwards: "We got off to a good start, but then conceded a goal on our mistake.
Rossi added: "Douglas Maicon did well on the Inter goal and it was a fast move, but Valon Behrami should have followed the run.
"I think Rocchi started his goal from an onside position, but then again I am biased! What I can complain about is Cristian Chivu's foul on Behrami that should have been a penalty."
Rossi admitted this week he hoped Inter would win the Scudetto and there was talk in the papers that Lazio would not put too much effort in, as a victory today would help rivals Roma close in on the title.
"We are a team who have always gone for the win, home or away, in Italy or Europe. I don't think it was fair to suggest beforehand we'd hold back, but it's part of the sport."
Inter coach Roberto Mancini said: "A victory would have been better, as it would've given us more breathing room, but the advantage remains pretty big and the number of games left is reduced to seven.
"I think this coming week and the next will be decisive."