Anyone who has taken a vacation knows that the first day back to work is the hardest. But getting back to your nine-to-five routine and climbing back into the ring are very different things.

WBO lightweight title holder Acelino Freitas (38-1, 32 KOs) makes his return to boxing tonight when he faces WBA lightweight champion Juan Diaz (31-0, 15 KOs) in a unification title fight after spending almost eight months away from the ring.

The 31-year-old Freitas announced his retirement from boxing last October after winning the vacant WBO title from Zahir Raheem almost exactly one year ago. That's a big reason oddsmakers had no other choice but to set the aging Brazilian as a +185 underdog for tonight's tilt against the young and impressive Diaz.

"If this bout happened a couple years ago, there would be little doubt that Freitas would have opened the betting as favorite," says linesmaker Joey Odessa. "Age catches up to everyone in the fight game and Freitas is battling a younger Diaz along with Father Time on Saturday night. The line reflects it."

Freitas marks the first true test for Diaz, the undefeated 23-year-old from Mexico. Diaz was held out of many big-name lightweight fights early in his career in order to polish his style and avoid the all-too-common quick burnout that has ruined many other young fighters.

The two boxers have contrasting styles. Diaz is a busy fighter who tries to overwhelm his opponents by throwing a lot of punches in order to bank early rounds and take decisions to the judges. On the other side, Freitas is known for his power and has taken 32 of his 38 professional wins by knockout.

"Freitas needs to get his respect early and slow [Diaz] down or it's going to be a long night for him," says Odessa. "The likely outcome would be a decision win for one of the fighters, but the venue and promotional advantage would have to favor Freitas. You can never tell what fight the judges are looking at."

The possibility of this fight going into the deeper rounds favors the fresh legs of Diaz, who has won more than half his fights by decision. He told reporters he trained for two different types of a fight for Saturday. One, in case Freitas resorts to his classic brawling style, and the second, in case the Brazilian adopts the more refined, patient method he's shown in his last three bouts.

The questions around Freitas' longevity started back in 2004 when he threw in the towel in the middle of the 10th round against Diego Corrales after getting knocked down three times. Now, three years later and three years older, those questions still haunt the Freitas, especially as he carries some ring rust into Saturday's fight.

"(The layoff) hasn't affected me at all because I have three gyms in Brazil and I am constantly in the gyms," Freitas told USA Today. "Knowing that I am going to face one of the top fighters in the world, I was always staying active in my gyms. So (the layoff) isn't going to affect me at all because I have already programmed myself to become the undisputed lightweight champion of the world."

Bettors can watch tonight's fight live on HBO's Boxing After Dark at 10 p.m. ET. Books have set Diaz by decision at +110, Freitas by TKO/KO at +350, and a draw at +1400.