Motorhead's hard-charging 'Ace of Spades' takes on Deep Purple's immortal 'Smoke on the Water' in round two of Ultimate Classic Rock's fan-voted March Riff Madness.

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

Motorhead already toppled one giant in this competition, handily defeating none other than Black Sabbath and 'Iron Man' in round one. They've got a similar challenge in store with Deep Purple, who previously beat out Judas Priest's 'Breaking the Law' without much difficulty.

So which of these iconic riffs deserves to advance? It's your choice! 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 Deep Purple Perform 'Smoke on the Water'