Montella claimed Fiorentina lacked penetration in the first half at the Stadio Olimpico and was thrilled with how they opened up Roma's defence more regularly in the second period.
Mario Gomez struck both goals for Fiorentina, deflecting Manuel Pasqual's cross inside the far post in the 65th minute, while the German striker brought down another of his team-mate's deliveries with a minute remaining before thrashing it into the roof of the net.
"In the first half we kept the ball well but were lacking penetration," Montella told ViolaChannel.
"After the restart we were much more determined and played more consistently."
Montella also hailed Gomez's performance after the 29-year-old struck his fifth goal in four matches in all competitions: "That's what we expect from Gomez. We know he's lethal in the box.
"We said the same things when he was being denied by the woodwork [earlier in the season]."
Gomez, who missed five league games earlier in the season with a hamstring injury, only managed one goal in his first 13 matches of the campaign.
But the one-time Germany international insisted he never lost faith in himself.
"I went through a tough spell but I spent almost a year on the sidelines," he told RAI.
"I needed to get my strength back before I could find my form of old and now that I'm fit again I'm having more of an impact. I never doubted my ability."
