What rap song starts out with the rapper saying Its Showtime?

Oh, dude, that's an easy one. The rap song you're thinking of is "Lose Yourself" by Eminem. It starts with him saying, "Look, if you had one shot, or one opportunity, to seize everything you ever wanted, in one moment, would you capture it, or just let it slip? Yo." So, like, that's the one you're looking for.