The striker converted a penalty against his old club after the Raphael Guerreiro opener.
“Our first half was not up to our usual standards, but not disastrous. We just gave away the goal on an error playing out from the back," Immobile told Sky Sport Italia.
“We did well to react and I particularly liked the last 20 minutes, when we tried to give everything to win the game. We wanted to secure qualification tonight, but it'll go down to the last match.
“I am happy to have scored, but I think the team deserved more than one point, so a defeat would've been truly painful.
“We have the right mentality, of a side that wants to win at all costs."