Sugar Ray Leonard beat "Roberto Duran" at his own game yesterday, knocking him out in the eighth round with a body punch.

Mike James of Hillcrest Heights, Md., a chunky 145-pounder who has won 75 of 85 amateur bouts, played Duran, because he is a stand-up boxer like the No. 1 contender from Panama. James was instructed to throw overhand rights, as is Duran's wont.

The remarkable aspect was that Leonard was wearing "pillows," 14-ounce sparring gloves. His hand speed figures to be of higher velocity on June 20, when he defends his World Boxing Council welterweight championship in Montreal, because the gloves will weigh eight ounces.

Before taking on James, Leonard sparred four rounds with his cousin, Leonard, at his training headquarters at the Sheraton Inn-Washington North-east in New Carrollton, with Odell simulating Duran's primitive aggressiveness.

In the third round against James' portrayal of Duran, Leonard was scoring the most with right leads.

James was making Leonard work hard with short, inside punches in the fourth round, which was actually Leonard's eighth. James got a rhythm going that positioned him to deliver the prescribed overhand rights, when the champion suddenly beat him to the punch with a left just under the heart.

The well-conditioned 18-year-old ended up on his back as if his nerves were paralyzed by what he later termed "a perfectly timed blow." When James failed to stir for several seconds Leonard's trainer, Dave Jacobs, went to his aid.

James asked Jacobs to remove his headgear "so I can get my breath."

After James rose, with help, Leonard asked spectators for applause for the sparring partner's painful contribution to his conditioning.

James said he had never been knocked down before by a body blow.

Leonard said of the obvious difference in the caliber of punching ability between James and Duran, "I am not going to be standing still and letting Duran hit me with right hands. I'm going to upset him with my tactics; he's very temperamental. I'm going to drive him crazy. That was a small ring today; wait until I get room in a bigger one, where I can move.

"Duran has never been hit to the body like I will hit him. Wait until I hit him six or seven times like I did Mike (James). Carlos Palomino stood straight up and took right hands; I think he was overawed by Duran.

"Duran has the pressure on him; I'm the champion and he has to take the title away from me, decisively. He was perspiring from the pressure at the news conference in New York.

"When I win I just want my critics to say I beat Duran, not an old Duran, not an ancient Duran who was the best in the world, just Roberto Duran."