The Nerazzurri were denied the chance to move up to third in the table when Renan Garcia's late goal found its way into the back of the net.
"I'll be honest, the way I see football this was our worst performance of the season. We went too deep after going 1-0 up, though even then we hadn't started that well," he told Sky Sport Italia.
"We had several chances to finish off the game with Fredy Guarin hitting the post, but we weren't ruthless enough. A great team must bring something extra out to put the result beyond doubt.
"We were far too inconsistent and only held control for five minutes at a time. We were distracted, pushed forward sporadically and I saw a different level of concentration to our usual standards. We must reflect on that and not do it again."
Today's result means that Inter remain in fourth place in the Serie A table.