If motivation has been B.J. Penn’s biggest challenge, it shouldn’t be one for this fight.

The former UFC lightweight and welterweight champion rekindles his most famous feud when he meets Matt Hughes in a rubber match at UFC 123 tonight in Detroit.

The two share a history dating back to 2004, when Penn, who had fought at 155 pounds his entire career, moved up to welterweight and beat Hughes for the title.

Hughes, a multiple-time world champion, had won six straight fights at 170 pounds before the loss to Penn. He went on to win six in a row after that, including a rematch with Penn in 2006.

With no title implications, tonight’s fight represents a chance for both men to prove they are the superior fighter.

"We’re both competitive guys and I think we both wanted it," Hughes said during last week’s UFC conference call. "B.J. and I are a lot alike in that we’ve split one (fight) and we finally get this third match, the rubber match."

It’s a good fight for Penn, who has withstood criticism following consecutive losses to Frankie Edgar this year, ending his run as the sport’s most dominant lightweight champion.

Penn looked uninspired in August’s loss, but wasted no time getting back in the gym and moving forward.

"I was kind of bummed out on my way home after the (Edgar) fight, but I didn’t really get banged up or bruised up too much, so I just kind of jumped back in the gym on Monday and started training," Penn said.

After a rematch with Kenny Florian fell through the cracks, the opportunity to fight Hughes presented itself.

Penn’s lost his past three fights at 170 pounds — once to Hughes and twice to current champion Georges St-Pierre — but isn’t concerned about the move to a higher weight.

"A lot of people are doing it; I’m not the only guy," Penn said about the move in weight classes. "I feel like I haven’t missed a beat. I feel like it was just yesterday when I was fighting at welterweight."

The 37-year-old Hughes has one of the most impressive resumes in the sport, posting a 45-7 record. A loss to Penn would mean much more than simply adding a loss to his career record.

"The way I feel is if I were to lose this fight to B.J., it’s like losing three fights," Hughes said. "But if I win this fight, it’s like winning three fights. It’s the final of a trilogy. There’s a lot on the line."

For Penn, it’d actually be a three-fight losing streak, something he’s never had in his career. His overall record (15-7) comes nowhere close to Hughes’, but their status as the sport’s all-time greats is the same.

"B.J.’s fought nothing but the best," Hughes said. "Look at his last fight with GSP. I mean, he’s always done well no matter what weight class he’s at."

Penn’s motivation has been called into question throughout his career, including after his previous fight when he lost all five rounds to Edgar in a lopsided decision.

Returning to his hometown of Hilo following the fight, Penn got a quick taste of life without the UFC and was eager to get back in the ring.

"There’s not much to do in Hilo, and when I got home after the fight there was a couple of days I didn’t have anything to do," Penn said. "Once you’ve been where (we’ve) been, a lot of other stuff just seems boring.

"(UFC president) Dana (White) gave me the text saying if (I) wanted to fight Matt Hughes and I just started shaking all over my body. I was like I’ve got a reason to live for a couple more months."

Hughes and Penn will be the co-main event today. The headliner is a light heavyweight fight between former champions Quinton "Rampage" Jackson and Lyoto Machida.