The Giallorossi threw away a 2-0 lead and only won thanks to a soft penalty, while 10-man Lecce threatened an equaliser late on.
"All we can do is not make any mistakes and hope our rivals run into difficulty. We are convinced that we can catch up to the others," said Domenichini, in for the suspended Luciano Spalletti.
This was hardly a vintage performance and the Stadio Olimpico crowd jeered on occasions when they were under pressure.
"We can't seem to keep a cool head when we have the lead and that creates problems. We need to work on it, as this is no way to approach the game. Many players aren't on top form, but I think it's a psychological issue.
"Mistakes were made, we stretched out and Lecce took advantage. These things should not happen and we didn't keep pressure on them in midfield after going 2-0 up, sparking a chain reaction."