It didn't take long for Richard "Hard Face" Mason to acclimate himself to the heavyweight division. Three minutes to feel his way around, then three minutes to demolish Rick Keller in the main event of last night's monthly boxing card at the Holiday Inn Crowne Plaza in Rockville.

Mason, a world-ranked cruiserweight fighting as a heavyweight for the first time, floored Keller three times in the second round of their 10-round bout. The last knockdown, which occurred one second before the bell rang, failed to draw a count from referee Milt Green, who stopped the fight immediately.

Even in victory, Mason (16-2-1, 12 knockouts) wasn't satisfied with his performance against an opponent known more for his lopsided record -- Keller, of Council Bluffs, Iowa, fell to 23-27-2 with the loss -- than anything else. Then again, Mason had no reason to be disappointed, as Keller, 35, had knocked out each of the five cruiserweights he had faced.

"It really wasn't what I expected," said Mason, 23, who spent most of the fight trying to break away from Keller's holding. "I don't mind fighting as a heavyweight, as long as I'm a full-fledged heavyweight. {Keller} had me by 25 pounds."

Keller, weighing 216 1/2 pounds, might have been heavier, but that was the only advantage he had over Mason, who weighed 191 1/2. The Cincinnati native dropped Keller midway through the second round with a right hook, then floored him with a left hook about 20 seconds later. The end came shortly thereafter as Mason, the International Boxing Federation's fifth-ranked cruiserweight, again scored with a left hook.

"I {don't} know what his manager plans to do next, but we'll keep him busy," said Emile Griffith, the former six-time world champion who trains Mason. "This is the second time I've worked with Richard, and we seem to be getting along pretty {well}."

Don Elbaum, Mason's promoter and manager, said Mason likely will fight for the vacant United States Boxing Association cruiserweight title this fall, possibly in August or September.

"He's got it," Elbaum said. "It's just a matter of who else is in the ring."

Elbaum's main attraction, IBF welterweight champion Simon Brown, trained Germantown resident Benny Collins for his professional debut, but Collins lost a four-round unanimous decision to Hagerstown's Luke Cooper (2-0) in a junior welterweight bout.

"I was very encouraged by the performance," Brown said of Collins. "He was moving like I told him to do. All I wanted was a little more of him letting his hands go."

Rockville's Phil Gilberti (10-4) scored a first-round technical knockout of Elliott Levine (0-2) of Masontown, Pa., in a six-round heavyweight bout to keep alive his dubious streak: each of Gilberti's 14 fights has been decided via knockout.

In other preliminary fights, Rockville's Les Johnson (4-0) won a unanimous decision over Frederick's Chris Lucas (2-4-2) in a four-round junior middleweight bout, and Jason Waller (3-0) of Stafford, Va., scored a first-round technical knockout of Jeff Schmude (0-1) of Erie, Pa. in a four-round light heavyweight bout.