Roberto Mancini suffered his first defeat since returning as Inter head coach last weekend in a 4-2 setback to Roma at the Stadio Olimpico.
There were plenty of positives for the Milanese side in that fixture, though, as goals from Andrea Ranocchia and Pablo Daniel Osvaldo twice restored parity after they fell behind.
Inter's inconsistent form this season has left them in 11th place after 13 matches, but just six points separate them from third-place Napoli and a UEFA Champions League spot.
"There is a feeling that we can fight for third place," he told Gazzetta dello Sport. "In Rome we have shown we play against anyone, because we went to their stadium and we scored two goals, twice recovering the disadvantage.
"We showed character and, with less naivety at 2-2, we would have obtained a positive result.
"This gives me a lot of confidence and as long as the math does not condemn us, I will fight for third place."
The former Manchester City boss' second coaching bow started on home turf in the Milan derby, but that fixture - which finished 1-1 - was a designated home match for Milan.
""They are one of the most loved clubs in Italy and I can't deny that a little piece of my heart is still in Milan," he said.
"We are going to San Siro with our heads high. It will be a difficult match because Inter are starting to play better."
