Michelle Williams is really heating things up as Marilyn Monroe!

The 31-year-old actress transforms into the Hollywood icon in the upcoming flick "My Week with Marilyn" -- and now we're getting our first look at her performing a classic Monroe song, "Heat Wave" from "There's No Business Like Show Business."

Check out Marilyn singing the same song in the 1954 movie below to compare -- how do you think she did? Sounds (and looks!) pretty good to us.