Merriam-Webster gives 'nearly' as one of the definitiions of 'near', so there are cases where the two are virtually equivalent. The example given in that dictionary does not hyphenate as you have done, however: The plant was near dead when I got it. So you need "a near perfect performance" for your second phrase.
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PamQueueDoes the hyphen force "near" and "perfect" to be read together, so that "near" is an adjective inNo. near is an adverb in both case
"a near-perfect performance"
, but without the hyphen between "near" and "perfect", "near" becomes an adverb and modifies "perfect performance" in
"a near perfect performance"
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