While Nick Diaz vs. B.J. Penn at UFC 137 is the new headliner, it's not going to be for five, five-minute rounds. According to UFC President Dana White, because that bout was originally slated to be three rounds and there are only eleven days until the fight, the new main event will still be contested along originally agreed upon contractual terms.
"We kind of want to make it a five-rounder," Gracie said.
UFC officials announced the implementation of five-round non-title fights earlier this year for all future non-championship main events. That rule can be amended if circumstances arise that hamper the preparation time of fighters. ...
"This kind of proves he's ready to [fight for the title]," Gracie said. "We really want it to show that Nick is ready."
"If you can't go five rounds, how are you going to fight GSP?" he said.
If both fighters lobby hard enough, it's conceivable White would be amenable to change. Among fighter interest, the likely ability of both fighters to competently fight five rounds and the need to please disappointed fans, the door remains open if both fighters want it.
Two more considerations. You'll recall Diaz was originally training for a five-round fight against Georges St. Pierre before he was pulled from the main event. Second, a longer fight favors Diaz as his physical durability, patient-patented style and superb conditioning make him a stronger threat later in the fight. Penn, on occasion, has also demonstrated conditioning issues in later moments, although he's also proven to be able to capably fight the distance and win against credible opposition.