Excuse me while I roll my eyes…
Writing with speed instead of quickly to avoid being a “bad writer” by using an adverb is cheating. It’s also awkward and ridiculous (which is why I’m, y’know, ridiculing it).
Fun fact: If a word modifies a verb, it is functioning as an adverb, whether it actually is one or not, and regardless of what grammatical contortions are attempted to avoid that.
The garage door opened quickly, and suddenly they were face to face.
Consider deleting suddenly, though, because it isn’t necessary, and replacing it with then (which is also an adverb, by the way — not all adverbs end in –ly). Another option would be to delete quickly and let suddenly do all the work. Or change the sentence to The garage door opened suddenly, and they found themselves face to face.