Walter Mazzarri's men struggled to cause Milan any noteworthy problems and Nigel de Jong's winner midway through the second half condemned the Nerazzurri to a narrow defeat.
"This wasn't a great derby, one moment could have decided it and it went their way unfortunately," Ranocchia told the official Inter website.
"It was a tight match like the first one this season. That day the moment went our way, tonight it went for them.
"They hit the bar through Kaka, but apart from that it was a bad game.
"We tried but going behind in a derby away from home created a tricky atmosphere and we weren't able to react."
Inter remain fifth in Serie A with 57 points from 36 games.