Cengiz Under and Edin Dzeko were both on the scoresheet for the triumph.
“All the lads had a good match, especially in the first half, when we were almost perfect," Fonseca told Sky Sport Italia.
“We should not have conceded that goal right on the stroke of half-time, but other than that, we did well. We know what we did wrong against Torino and Juventus, as we lost, but we also created lots of scoring opportunities, so there was no need to lose confidence.
“This team creates chances, but we mustn't make these mistakes with the final pass."