UFC 178 fight card primer: Johnson vs. Cariaso, Kennedy vs. Romero, and Zingano vs. Nunes

Tonight is a highly promising night for MMA fans, as UFC 178 takes place in Las Vegas, Nevada, where Demetrious Johnson defends his flyweight title against heavy underdog Chris Cariaso. The co-main event sees Donald Cerrone welcome Eddie Alvarez to the Octagon, while Irish featherweight rising star Conor McGregor takes on Dustin Poirier.

With the main event widely considered to be a mismatch and a big downgrade from the anticipated Jon Jones/Daniel Cormier, it feels like the "real" main events are Poirier-McGregor and Cerrone-Alvarez. So this primer looks at the main event plus the opening two main card matches. The UFC 178 PPV broadcast starts at 10 PM ET/7 PM PT and is preceded by the preliminary card on Fox Sports 1 at 8 PM ET/5 PM PT.

Demetrious Johnson (20-2-1 MMA, 8-1-1 UFC) vs. Chris Cariaso (17-5 MMA, 7-3 UFC) - UFC Flyweight Championship

Mighty Mouse has been nothing short of superb since capturing the inaugural belt back in 2012. Aside from a rough first two rounds against John Dodson in his first defense, Johnson has looked damn near unbeatable. His career highlight is obviously the shocking 1st round KO of Joseph Benavidez last December. After that surprise outcome, Johnson easily dispatched Ali Bagautinov in what stands to date as his only fight in 2014.

Cariaso has found his calling at flyweight in 2012, defeating Josh Ferguson in his debut at the weight class. Consecutive losses to John Moraga and Jussier Formiga knocked him down the pecking order, but the 33-year-old has strung together consecutive wins over Iliarde Santos, Danny Martinez, and Louis Smolka to get his title shot, however questionable it may be. As good as the winning streak has been, none of the fighters he's beaten is ranked, so the extraordinarily low odds of him getting the upset are more than justified, so it's up to him to prove the doubters (and oddsmakers) wrong.

Tim Kennedy (18-4 MMA, 3-0 UFC) vs. Yoel Romero (8-1 MMA, 4-0 UFC) - Middleweights

Who knows what could've happened if Tim Kennedy had not beaten Roger Gracie in his UFC debut? Gracie was released, but maybe Kennedy would've seen a similar fate if the outcome was different. After Kennedy took care of Roger, he KO'd Rafael Natal in front of his fellow military brethren in Kentucky. Pegged as an underdog against Michael Bisping, the former Strikeforce title challenger was able to outwork, outstrike, and outwrestle Bisping en route to an upset unanimous decision win. If he gets past Romero it's quite possible that he'll need only one more win to secure a title shot.

Romero underwhelmed in Strikeforce when he fought Rafael Cavalcante, displaying a puzzling lack of offense before getting KO'd by "Feijao". A drop to middleweight has paid off brilliantly for the Cuban Olympic medallist in freestyle wrestling, as he's won all of his bouts since the Feijao defeat. His biggest win to date is a near-cartoonish thrashing of Brad Tavares in April, which has earned him a meeting with a clear top 10 middleweight in Kennedy.

Cat Zingano (8-0 MMA, 1-0 UFC) vs. Amanda Nunes (9-3 MMA, 2-0 UFC) - Women's Bantamweights

The PPV kicks off with the return of the undefeated Cat Zingano, who saw her title shot vs. Ronda Rousey go up in smoke when she blew out her knee. Miesha Tate, who Zingano defeated by 3rd round TKO in April 2013, snagged her coaching gig on TUF 18 and the title fight. For Zingano, it's been a story of recovery both on a physical and personal level, and with a win over Nunes tonight she will be next for Rousey.

Nunes hasn't had too many fights herself inside the Octagon, but when she has competed she's been dominant. The Brazilian easily took care of the rather one-dimensional Sheila Gaff with some wicked ground-and-pound, and then pulled off the same TKO feat against Dutch striker Germaine de Randamie. Now that she's healthy again she can play the role of spoiler against the consensus #1 contender.