Stephan Bonnar and Anderson Silva will meet in an unexpected main event.
Bonnar enters as a steep underdog against the pound-for-pound best fighter on the planet.
With four-ounce gloves anything can happen, and Bonnar certainly has the skills to pull off the incredible upset in Silva's backyard. Odds go out the window when the cage door shuts.
This could be the capstone of Bonnar's long career, and possibly send him off to retirement on an all-time high. If he is the man to defeat Silva in the UFC he will go down in the history books much the same as Matt Serra did for defeating GSP.
Here are three keys to one of the biggest upsets in MMA history.