LAS VEGAS — Tonight's UFC 74 event presents one of the top fight cards of the year.

Here are five storylines worth checking out on the pay-per-view event from the Mandalay Bay Events Center:

1. Can Gabriel Gonzaga become the next big thing?

Since a knockout victory of a seemingly indestructible Mirko "Cro Cop" Filipovic at UFC 70, Gonzaga has become the UFC's overnight sensation.

At tonight's UFC 74 main event, he'll take on UFC Hall of Famer and current 44-year-old heavyweight champion Randy Couture.

While Couture has nothing left to prove in his illustrious career, Gonzaga is trying to prove his latest victory was no fluke.

He can do just that with a victory in tonight's title fight.

2. Can Georges St. Pierre prove his mental toughness?

No one doubts St. Pierre's athletic ability, but ever since a stunning first-round TKO loss to Matt Serra at UFC 69, the former champ's mental toughness has been a whole other story.

St. Pierre, who was once dubbed the UFC's top pound-for-pound fighter by fans, has since been labeled a head case and mentally weak — after just one lousy loss.

The Canadian now faces Josh Koscheck, a former NCAA Division I wrestling champion and a top welterweight contender. St. Pierre can silence the critics with a convincing victory.

3. Will Joe Stevenson keep his title hopes alive?

The UFC's lightweight title picture is blurry thanks to current champ Sean Sherk's failed UFC 73 drug test and pending appeal. His hearing is scheduled for October, and if the suspension sticks, UFC president Dana White says he'll have no choice but to strip Sherk of the title.

That leaves a host of 155-pound hopefuls, including Joe Stevenson, eager for a shot at the possibly vacant title.

With a 27-7 record (4-1 mark in the UFC), Stevenson could earn consideration if he shuts down Brazilian jiu-jitsu black belt Kurt Pellegrino tonight.

It would be Stevenson's 13th win his past 14 fights.

4. Is this is it for Frank Mir?

When he won the UFC's heavyweight title in 2004, Frank Mir was considered the future of the division: a solid striker with an even better ground game. But three months after winning the title, Mir was involved in a devastating motorcycle accident that kept him out of action for two years.

Although his return has been nothing short of miraculous, the results have been far from spectacular. He's gone 1-2 in three lackluster performances.

He'll now take on a beatable Antoni Hardonk on tonight's undercard. Another loss could spell the disaster for Mir's once-promising career.

5. Will Las Vegas sell out an event?

With the UFC's boom in popularity, the world's No. 1 mixed-martial-arts organization has strayed from its Las Vegas home more and more often. Any why not? While the organization has sometimes struggled to sell out the modestly sized Mandalay Bay Events Center in Sin City, locations such as Columbus and Houston have packed records crowds into major venues.

Tonight, the organization returns to Vegas with one of the year's best fight cards. If the local crowds again fail to arrive, Midwest and international cities could be the ones that benefit.

Dann Stupp is editor-in-chief of UFCjunkie.com, which is an associate MMA partner of Yahoo! Sports. For the latest MMA and UFC news, go to www.ufcjunkie.com.