It's a cross-generational battle as the Doobie Brothers' 'China Grove' vies with Motley Crue's 'Kickstart My Heart' for the right to advance in Ultimate Classic Rock's March Riff Madness.

In a contentious process that somehow only resulted in one actual fist-fight, we’ve selected 32 of classic rock’s most iconic riffs and paired them off in 16 first-round duels. Over the next five weeks the field will be repeatedly cut in half by your votes, until we theoretically arrive at the most awesome riff in rock history.

The distinctive, staccato opening riff of 'China Grove' was first heard on the Doobies' 1973 album 'The Captain and Me,' and to this day they'd be fools not to include it in each and every one of their set lists.

The adrenaline-boosting riff of 'Kickstart My Heart' debuted on Motley Crue's 1989 smash hit album 'Dr. Feelgood' and continues to rear its head throughout modern culture -- appearing in a 2012 Super Bowl commercial and more recently just about ruining a big-league baseball game.

So who will win this battle? It's your call. You can vote once per hour until round one of our March Riff Madness voting closes on Sunday, March 9 at 11:59PM ET. The ultimate winner will be revealed on April 7.

Watch the Doobie Brothers Perform 'China Grove'

Watch the Doobie Brothers Perform 'Kickstart My Heart'