BOSTON » A win earns Frankie Edgar the proper respect as a champion.

A victory keeps B.J. Penn relevant.

Who has more on the line?

Something has to give tonight in the main event of UFC 118 at the TD Garden, where Penn tries to avenge his only loss at lightweight in more than eight years.

Since the first fight, a disputed decision victory for Edgar, both men have had to answer a lot of questions.

Edgar has had to defend the victory in which he relied on the judges to pull out the stunning upset to win his first UFC world title.

For Penn, who will compete in his 11th title fight, he’s had to take criticism for a lackluster performance in a fight he entered as an 8-1 favorite.

"That’s why we did this fight," UFC president Dana White said.

Penn’s career goes one of two ways when the fight is over. He’ll either reclaim his status as the best in the world at 155 pounds — and get the opportunity to continue to fight the top lightweights in the world — or be in unfamiliar territory. The 31-year-old black belt in jiu-jitsu won’t be a world champion, won’t be on track toward a world title shot and his customary spot at the top of UFC PPV events might go by the wayside.

"You never know with B.J. Penn," White said. "If that happens to him, he might say it’s time to retire.

"Or it might light a fire under him to go back and say I’m (expletive) back, man. I’ve been waiting for that B.J. Penn forever."

White may have his wish after Penn suffered the worst loss of his career to Georges St-Pierre in January 2009. He bounced back, under a new training regimen, with back-to-back dominant performances against Kenny Florian and Diego Sanchez, sealing his status as the sport’s best lightweight.

Trainer Marv Marinovich, father of former NFL quarterback Todd, worked with Penn during those two victories, but was not asked back for the Edgar fight, in which Penn fatigued in the later rounds.

After telling ESPN on Thursday that he "rested hard" for this fight, questions about his conditioning immediately came to the forefront.

He weighed in at 154 pounds yesterday, one below the limit, and says he’s in good enough shape to go a full 25 minutes, even if it isn’t the game plan.

"I’m a guy going out there to finish the fight," Penn said. "I feel I can be more busy out there and make some tweaks and adjustments."

The obvious difference from the first fight is for Penn to go to the ground, where his jiu-jitsu skills could pose problems for Edgar.

The champion expects that to happen, but at the same time, he wasn’t about to offer any predictions on how the fight is going to go.

"It might go to the ground a little, but you never know how it will play out," Edgar said on Thursday. "All I can do is focus on myself and what I do out there."

If Edgar can pull out a second win, even as a 3-1 underdog despite winning the first bout, it’ll mark the end of an unbelievable run for Penn.

He arrived on the scene with an impressive mix of stand-up and jiu-jitsu skills that saw him win his first three UFC fights by TKO. He stunned Matt Hughes to win the welterweight title and beat Joe Stevenson in 2008 to join Randy Couture as the only men to hold world titles in two different weight classes.

He talked a lot on Wednesday about wanting to continue to fight the best, but a second loss to Edgar could mean any number of things toward his future.

"I don’t want this to be my last fight," Penn said late last month in Hawaii before finishing up his training camp in California. "I want to stick around, I want to do this for a while, and I really am not thinking about losing at all."