"Something worked perfectly" vs "something worked perfect"

While grammatically the former one seems to be the only correct form (English is my second language, so let me know if I'm wrong here), the latter one appears to be used quite extensively, and I wonder if it's appropriate, too. Thanks!

This is a common mistake of (mainly native speakers) today to use adjectives in this improper way, as in your example. There's no grammatical reason to do so, but unfortunately it's happening more and more, even in mainstream media, TV, radio, etc.

I'm adding a quotation from an article called "Do it Real Quick, Or The Death of the Adverb". Beware that I do not necessarily agree with the whole article (in case you decide to read it), but I definitely agree with this quoted part:

Adverbs are on the retreat in Modern English. Do it real quick has become the norm. We want to get this bridge rebuilt as quick as possible is a borderline case (quickly seems to be more appropriate). But it is enough to listen to the people around us, to observe adjectives replacing adverbs. A boy of ten comments on the speech of a person with an accent: “You are talking funny.” As ill luck would have it, the adverb funnily is rare, so that the boy had little choice. To a conservative taste he did it real good is a bit too much, but I fully realized what odds adverbs are facing only when I read in an undergraduate paper: “She sings beautiful.” On the same day I heard: “She is fragile and walks slow.”

Perfect has been used as adverb since the fifteenth century, but such use is now non-standard.