Play video content EXCLUSIVE TMZ.com

Mariah Carey is unreal ... we got audio of her full dress rehearsal for her Vegas show which opens tonight, and she sounds as good as she did in 1990 when she hit #1 with "Vision of Love."

Mariah performed for more than an hour Monday night to a packed house at The Colosseum at Caesar's Palace, and you gotta hear it. She hits every high note and sounds flawless.

We got audio from someone in the audience ... filled with various people who work in Vegas-related businesses. We posted a minute-and-a-half and sampled 4 songs. Wait till you hear her hit the high notes in "Emotions."