Riccardo Orsolini's 94th minute winner means that Inter Milan is now equal to points with Napoli of Antonio Conte in the race for the Serie A title.
The two parties are both at 71 points of their 33 League matches, although stays on the top with a target difference of +40, 13 more than that of Napoli.
Barella, 28,, however, refused to reflect on the defeat and remains convinced that his side will end the season well.
“A defeat is always difficult to swallow,” Barella told Sky Sport Italia.
“We have many matches and there is fatigue, but that is not an excuse. It is not normal for a team like ours to give our goal when it is seven against three in the penalty area. We have to do better, football is ruthless.”
Treble Dreams who are still alive for Inter Milan and Nicolo Barella
Inter remains in the fight to win a remarkable Treble while they prepare for Barcelona in the semi -final of the Champions League, and arch -rival AC Milan in the semi -final of Coppa Italia on Wednesday.
“We should never have the feeling that we have already arrived, so we always have something that we can do better,” Barella continued.
“We fight on three fronts, we give ourselves everything, and these setbacks are painful. It was a balanced game and a draw would have been a fairer result. Nothing is still over, we are still at the top of the table next to Napoli.
“It will be a tough fight, but we want to fight on all fronts and will certainly not stop here.”