Floyd Mayweather promises better action in fight against Andre Berto

The haters have left the building.

Floyd Mayweather Jr., by defeating all of the major threats who could stop his pursuit of an unbeaten record at retirement, pounded his chest and pointed to a supportive crowd Friday before weighing in at 146 pounds for what he says will be his final fight.

For the first time in a long time, cheers for the 38-year-old Mayweather (48-0, 26 knockouts) out-sounded the boos among a scaled-down MGM Grand Garden Arena crowd generously estimated at 6,000.

Part of the response also has to do with apathy at Mayweather’s opponent, 30-to-1 underdog Andre Berto, who weighed in at 145 pounds for the welterweight title bout that will be shown on Showtime pay-per-view.

“Last time I’m ever getting on a scale. I want to thank all the fans in here,” Mayweather said. “I can’t wait to get out there and give the fans some excitement.”

Mayweather, coming off a sharp but roundly panned technical performance in May while beating Manny Pacquiao by unanimous decision in their long-anticipated meeting, promised improved action against Berto (30-3, 23 KOs), a former welterweight champion.

“He’s another tough guy with a high knockout ratio, a rugged competitor,” Mayweather said of Berto. “But I’ve faced everybody in the sport of boxing — Pacquiao, [Miguel] Cotto, ‘Canelo’ [Alvarez] — I’ve already faced the best fighters.

“The main thing is being at my best. Since Pacquiao didn’t give the fans a good fight, [Saturday’s] going to be a great fight.”

Berto, 32, crossed his arms and slightly brushed Mayweather during their weigh-in face-off pose.

“We’re here for a reason,” said Berto, who overcame a career-threatening shoulder injury in 2013 to knock out Josesito Lopez in March. “I’ve been through a lot. To come where I come from [Haiti], we never had a chance to come out of that. To tell you that I’m here tells you something.”

Mayweather hasn’t knocked anyone out since doing so to Victor Ortiz in 2011 with surprise punches off a fourth-round break in the action.

In Berto, he’s fighting a forward-coming fighter who was knocked down twice in both of his losses to Ortiz and Robert Guerrero, another foe who was dominated by Mayweather in a 2013 unanimous decision.

“I’ve been here before. I know what it takes,” Mayweather said. “Just stay focused. Stay on a parallel path. Go out there and do what I do best, and that’s win.”

Mayweather has found motivation for the apparent one-sided bout by insisting he will retire after Saturday night, the final of his six Showtime fights in a deal that’s generated $750 million from nearly 10 million pay-per-view buys.

“My game plan was to become a household name. I did that,” Mayweather said this week. “I just want to go do my job, be the best at what I do. Everyone’s talking about, ‘Oh, this will be my last … .’ I’ll talk to you guys again. I’m older, wiser, more savvy. I know when to fold, I know when to hold.”

As usual in a Mayweather fight week, he found himself deflecting criticism.

This time, it came from an SB Nation story that detailed how the U.S. Anti-Doping Agency allowed him a retroactive therapeutic-use exemption for a substantial IV of saline, multivitamins and Vitamin C to deal with dehydration immediately after he weighed in May 1 for the Pacquiao fight.

USADA didn’t notify the Nevada State Athletic Commission and the Pacquiao camp of the IV until days after the fight, outraging both.

Pacquiao was denied an injection of the anti-inflammatory medication Toradol on fight night because USADA, which oversaw drug screening for the bout, failed to inform the commission it would allow the injection.

“It seems like there’s a double standard,” Pacquiao business manager Michael Koncz said.

Pacquiao told reporters in the Philippines on Friday that he was “vindicated” by the IV news, and requested a rematch with Mayweather in a bout with “no favoritism … one where the Mayweather camp [doesn’t get] to dictate all the terms and conditions.”

Mayweather was asked about Pacquiao’s rematch request, and returned to evasion.

“I’m with Showtime. I’m only focused on Showtime fighters,” he said.

lance.pugmire@latimes.com

Twitter: @latimespugmire