The Frenchman inherited a club low on confidence after the loss to the Biancocelesti, but he feels it is back on track thanks to its sensational start to the current campaign.
The Giallorossi were beaten 1-0 by their city rivals at their shared home at the Stadio Olimpico in May, ending their hopes of securing European football for the 2013-14 campaign.
Garcia took charge in the summer, however, and has overseen a dramatic transformation in Roma's fortunes, with the club currently second in the Serie A standings, thanks primarily to a remarkable 10-game winning run at the start of the season.
"When I arrived the club was very unhappy and disillusioned. There was real heartache," the 49-year-old Frenchman told la Voix du Nord. "I worked on the psychological side with the players - it was a priority. The winning run was amazing and the more we won, the more it inspired us to keep it going.
"We could've won our last three games too [instead of drawing them]. We are [a point] behind Juventus, who are exceptional, but our target is just to get into Europe next season."
Garcia also sang the praises of Roma legend Francesco Totti, admitting that he is astounded by the passion the 37-year-old forward still has for the game.
"The first player I sent a message to when I arrived at the club was Francesco," the former Lille boss said.
"He is such a humble guy and a great player. I wanted to know if he was still hungry at 37 and he told me he was. He has proved that this season."