Sugar Ray Leonard walked through Hector Diaz like a swinging door in the second round of their welterweight fight before more than 7,000 persons at the D.C. Armony last night.

Leonard fought tentatively, even gently, for the bout's first five minutes as the examined the style of the unknown Diaz.

But late in the second round Leonard threw a right counter the Dominican walked flush into. The next 20 seconds were a blur, as Leonard hit Diaz with a barrage of punches.

At 2:20 of the second round Diaz was slumped in his corner, at the feet of his manager Woodrow Wilson Larroseaux with dared and puzzled look on his face and a large black eye.

Even Leonard could not remember half of the haymakers with which he staggered Diaz. "I hit him with everything," said the Palmer Park Olympic champion who was fighting in Washington for the first time in his year-old pro career. This victory made his record 6-0.

"The right hand started it. And it was a left hook that shoved him into his corner. After that you'd have to start counting (the blows). When I start throwing combinations I don't remember them afterward. But it sure feels nice."

Leonard's knockout was the first serious flurry of the fight and further added to doubts regarding Diaz" abilities.

ABC canceled its national telecast of this bout late Friday evening, claiming its week-long investigation had revealed that Diaz had not won a fight in more than four years. Also there was no evidence to show Diaz had fought anyone in 19 months. ABC said his record before the fight was 10-6-4.

Diaz looked cagey and experienced in his five upright minutes. He set a delibrate pace, showed a quick hook and good reflexes. However, he seemed to lack the strength of a fighter.

The surprisingly large crowd came to see Leonard demolish an object placed in his path and it got his wish. Leonard threw his hands over his head in joys as Diaz was counted out and the fans roared their approval of the 20 seconds of fury.

Perhaps Diaz' worst mistake was a willingness to fight once Leonard had tagged him. He tried to answer salvo for salvo and even caught Leonard with one low blow as the local hero charged.

That only incensed Leonard more and the end was sudden. Diaz staggered into his corner and simply waited, almost helpless, as Leonard raced across the ring and smashed him to the head with a rain of left hooks, overhand right and uppercut.

Leonard said ABC's pullout, and its charges that Diaz was not a worthy opponent, had "shocked me, but didn't bother me. This boxing is a business game, not just a sport. They have to do what they think is their business.

"But I was home tonight I fought home for the first time infront of my people and it was great. That's what matters. I'm not even going to say how many relatives I had here tonight."

One relative, his son, Ray Jr., was in his father's arms before Diaz was able to stand unaided.

This poor guy (Diaz) got hit by a right-hand counter sucker shot," said Angelo Dundee, Leonard's manager, who was upset at the rap on Diaz. "I know Diaz is a pretty good pro. He could have given a good fight if he didn't got tagged.

"Diaz maybe hasn't been getting enough work," added Dundee, "but that's a problem for a lot of guys. The sport just isn't healthy enough at the club level."

"The last day has all been confusion," said Diaz' manager. "People from ABC and everyone were grilling my fighter like to thief. He didn't sleep well last night. Sure, it upset him and hurt his fight."

This was Leonard's third straight knockout. As an amateur, Leonard was known for throwing as many kisses in the ring as KO punches.

"How has Ray been changing?" said manager Dave Jacobs. "He stoppin' 'em. cold."

In the aftermatch of the fight, Leonard's lawyer, Mike Traner, had no apology for Diaz as an opponent.

"Ray don't carry the guy. He went right after him," Trainer said. "Ray isn't going to be fighting top-ranked welterweights for a while. The thing that bothers us in all this is the tasteless fashion in which ABC handled its end.

"I talked with their (ABC) people today and they've gotten some of the flak for this that they deserved."

If ABC wasn't pleased, the crowd at the D.C. Armory was. For a few eyepopping moments, the home-town boy was the punching whirlwind they had come to see.