A hard-hitting battle is on tap as Motley Crue's 'Kickstart My Heart' takes on Metallica's 'Enter Sandman' for your votes -- and the right to advance out of round two of Ultimate Classic Rock's March Riff Madness.

32 of classic rock’s most iconic riffs were cut down to a field of 16 by your votes last week. We'll repeat this process four more times over the next month until we theoretically arrive at the most awesome riff in all of rock history.

Motley Crue -- who will embark on a farewell tour this summer -- survived a strong challenge from the Doobie Brothers' 'China Grove' in round one. Their reward? A duel with metal's biggest band, Metallica, whose 'Enter Sandman' defeated 'There's Only One Way to Rock' by Sammy Hagar.

So which of these titans gets to move on? It's up to you! Everyone can vote once per hour until round two of March Riff Madness closes on Sunday, March 16 at 11:59PM ET. The ultimate March Riff Madness winner will be revealed on Tuesday, April 7.

Watch Metallica Perform 'Enter Sandman'

Watch Motley Crue Perform 'Kickstart My Heart'