“If any fans know boxing, it’s D.C.,” Floyd Mayweather said at a press event in Washington on Tuesday. “You’ve always supported me.” (Jonathan Newton/THE WASHINGTON POST)

The line outside the Howard Theatre began forming before 6 a.m. Tuesday, and by the time the doors opened six hours later, it had snaked around the corner and down the block. Not even a typically hazy, hot and humid summer day in the District was going to keep devoted boxing fans from catching a glimpse of Floyd Mayweather or Canelo Alvarez.

Mayweather remains the undisputed pound-for-pound king and a guaranteed ratings bonanza each time he steps into the ring. At 36, the highest-paid athlete in the world is drawing even more interest among his devoted following as well as the casual boxing fan because his decorated career is by his own admission nearly complete.

Alvarez, meantime, has been rampaging through the junior middleweight division and become a hero in his home country of Mexico, where a six-figure attendance is expected when the sport’s most promising young fighter makes an appearance there Sunday.

On Tuesday afternoon, though, Mayweather and Alvarez, 22, were in the nation’s capital to promote their bout Sept. 14 in Las Vegas as part of an 11-city press tour that’s the most ambitious since Mayweather and Oscar de la Hoya stopped in 10 cities in advance of their record-setting fight six years ago.

“If any fans know boxing, it’s D.C.,” Mayweather, wearing all black with a diamond-encrusted chain around his neck, told the thousands of fans who occupied every seat. “You’ve always supported me.”

Mayweather (44-0, 26 knockouts) arrived in the District late Monday night after kicking off the press junket with Alvarez in New York’s Times Square. A friend picked up Mayweather at the airport, and the eight-time world title holder wound up shooting baskets with another friend at Dunbar High School to unwind in the wee hours.

Before being introduced on the main stage Tuesday, Mayweather and Alvarez spoke with reporters privately in a secluded area downstairs, and their styles could not have been more disparate. Alvarez (42-0-1, 30 KOs) delivered his answers through an interpreter in tones at times so hushed that he barely could be heard over the din of reporters and photographers.

That wasn’t an issue for Mayweather, who exuded the moxie that has put him squarely in the conversation as the greatest pound-for-pound fighter of all-time. His interview, which lasted nearly half an hour, covered what he expects from Alvarez in the fight at a catch weight of 152 pounds, but Mayweather also discussed his legacy and how he has limited some of the usual bravado.

“As you get older, you’re going to become a different person,” Mayweather said. “Sometimes they say every five years you become a different person, and if you don’t grow mentally, then it’s useless. You’re running in place. So you have to grow. Once you can’t grow physically, you’ve still got to grow mentally.”

That’s how Mayweather has carried himself in the ring, too. The most technically skilled fighter in the world is a master at outboxing an opponent rather than outslugging him, and that posture has served him well against challengers with notable physical advantages.

Robert Guerrero was one such recent opponent, but the California southpaw was no match for Mayweather May 4 at the MGM Grand in Las Vegas. Mayweather won by unanimous decision, with all three judges scoring the fight 117-111.

While Mayweather is moving up in weight this time, Alvarez is dropping two pounds to meet the requirements that have him in line for the most lucrative payday of his career. Alvarez said he did not want to move down in weight for this fight but agreed when Mayweather’s camp insisted.

Therein lies the first bit of controversy surrounding the fight.

“He’s a liar, his representation, his manager,” Leonard Ellberbe, a top Mayweather adviser, said of Alvarez.

Said Mayweather: “The way I look at it is this: He’s not forced to do anything he doesn’t want to do. We finally came up with something where both parties were happy, and then we made the fight happen.”