LAS VEGAS — The fact that they’re much bigger than when they first met eight years ago is undeniable. Both Manny Pacquiao and Juan Manuel Marquez have added bulk along with the pounds, and both have had to deal with those who suspect they didn’t do it naturally.

Along with the fighters, the purses and attention have grown as Pacquiao and Marquez meet tonight for the fourth — and presumably last — time in the rivalry that has served both fighters so well.

Marquez will try once again to do what he hasn’t been able to do in 36 evenly contested rounds against Pacquiao — get a decision from the ringside scorecards. At the age of 39, it’s a fight that may mean more to his legacy than his future career, which is why it’s a fight he seems almost desperate to win.

“All I ask is for the judges to be objective,” Marquez said. “They need to really see what is happening in the ring instead of what they think might be happening in the ring.”

Pacquiao is not as desperate, but he needs a win just as badly. He barely escaped with a majority decision over Marquez last November — a result that drew loud boos from the pro-Marquez crowd — and lost a widely panned decision to Timothy Bradley his last time out.

A loss to Marquez would not only confirm the whispers that he is slipping after 17 years as a pro, but perhaps derail for good any talk of a fight against Floyd Mayweather Jr.

“I have always been focused, but not like this fight,” Pacquiao said. “There are no distractions in my mind. The family problems I had I don’t have this time.”

Neither fighter holds a title as they meet in a welterweight fight that will make both even richer. Pacquiao is expected to make more than $20 million by the time the pay-per-view receipts are totaled, while promoter Bob Arum said Marquez could make as much as $6 million.

It’s a far cry from 2004, when Pacquiao and Marquez could barely fill half the arena. The fight, though, was plenty intriguing, with Pacquiao coming off a win over Marco Antonio Barrera that announced his entry into boxing’s elite and Marquez having stopped his past 11 opponents.

It seemed a mismatch when Pacquiao knocked his fellow 125-pounder down three times in the first round and Marquez barely survived to hear the bell. But the Mexican champion began a comeback in round 3, dominating the late rounds on his way to a disputed draw that foreshadowed what was to come in the years ahead.

All three fights — Pacquiao won the past two — were so close they could have gone either way.

Pacquiao might not have gotten the fight with Oscar De La Hoya that catapulted him to stardom in 2008 just nine months after beating Marquez in a split decision in their second fight. Marquez, meanwhile, might have become more than just an opponent getting rich off the names of fighters who will be judged better than him.

“My career maybe changed, and everything would be different,” Marquez said. “But I feel great what happened in the past with Manny.”

A fourth fight between two world class fighters is almost unheard of in a day when top fighters rarely enter the ring more than twice a year. Almost as astonishing is that they were spread out over eight years and five weight classes, yet tonight’s fight will still be a pay-per-view event that will likely draw more than 1 million buys (HBO $59.95) across the country.