Assuming his upcoming title fight at UFC 158 is a "guarantee," Nick Diaz has opened as a 4-to-1 underdog against Georges St. Pierre.

That's where the former Strikeforce Welterweight Champion, pegged at +330 in the betting lines, will try to capture St. Pierre's crown in a championship main event booked for the Bell Centre in Montreal on March 16, 2013. "Rush" opened as the -430 favorite, according to Best Fight Odds (via MMA Fighting).

At least for now.

Diaz (26-8) hasn't been this far down since he opened at +285 in his 170-pound match-up against B.J. Penn prior to the UFC 137 event in October 2011; however, that line shifted considerably and "The Prodigy" was only -135 by the time he stepped inside the cage.

Likewise for St. Pierre.

His opening line, similar to the odds for his Matt Serra rematch at UFC 83, is the highest it's been since his lopsided match-up against Dan Hardy at the UFC 111 extravaganza back in early 2010, where "Rush" started at -500 to "The Outlaw's" +300.

The highest opening for Diaz was -700 against Mike Aina under the EliteXC banner -- a fight he won by split decision.

As it stands, the UFC co-main event has Rory MacDonald at -175 to Carlos Condit's +135, despite the fact that "The Natural Born Killer" won their first go-round by way of technical knockout.

Well maniacs, those are the cold, hard numbers, which will undoubtedly change as we inch closer to the fight night pay-per-view. But in which direction? And how accurate do the opening lines reflect the match-up in your opinion?

To see how -- and why -- St. Pierre vs. Diaz was assembled for UFC 158 click here.