Spotify as default music source for Google Voice Command "play "song" by "band"

[david_rahrer]

I would have thought this a common question but I'm not having much luck. When I ask Google Now to play "song" by "band" or similar, it works fine but only uses Google Play to do so. I want it to use Spotify as the default as I only use GP as a basic mp3 player. Is this possible? I'm on a Moto G (1st Edition) with Lollipop 5.1.

I appreciate any direction on this. Thanks!