Suso, Hakan Calhanoglu and Nikola Kalinic were on target as Milan returned to winning ways in the league, having managed just one victory in six games in all competitions.
Montella, whose Milan are eighth and nine points behind Massimiliano Allegri's men, is now preparing for Saturday's visit of Juve with renewed belief.
"It's a victory that gives us belief and strength. We had already seen significant improvements in the quality of football over recent games and I am very satisfied with this performance," Montella told Mediaset Premium.
"I am already looking forward to Saturday's game with Juventus and we don't have much time to celebrate, even if we do want to enjoy the moment.
"We had a psychological block, all sorts of things happened and the team had to shake some things off. In the second half, the lads were more enterprising and I hope from now on these players will be able to express their immense talent with more freedom.
"I want to see the spark we're looking for and hope that Juve underestimate us a bit on Saturday."
Milan's drought-ending victory came in the absence of captain Leonardo Bonucci, who was sent off in the 0-0 draw at home to Genoa last week.
Asked if Milan benefited with the under-performing Bonucci sidelined, Montella replied: "You can criticise Bonucci for some performances, but can't put his quality in doubt, otherwise we may as well go and do a different profession."