Inter fought back from 2-0 down to snatch a 2-2 draw with Catania in the final minutes of last night's match.
"I am upset, although in these important stadiums with world class players, they can change the game in only a few minutes," said Montella.
"Unfortunately we were perfect for 75 minutes and in the second half failed to take our chances. We lowered the tempo and in a game like this it means you risk losing, such as Giampaolo Pazzini's late opportunity.
"The first half was fantastic, as we played so well and allowed Inter nothing, hitting them in the right moments with team counter-attacks."