ATLANTIC CITY, N.J. (AP) _ Mike Tyson, 221, New York, stopped Alex Stewart, 221, New York, at 2:27 of the first round, heavyweights; Julio Cesar Chavez, Mexico, stopped Kyung Duk- Ahn, South Korea, 3, to retain his WBC super lightweight and IBF junior welterweight titles; Donovan ''Razor'' Ruddock, 228, Canada, knocked out Mike Rouse, 228, Portsmouth, Va., at 2:37 of the first round, heavyweights; Tyrell Biggs, 228, Philadelphia, outpointed Rodolfo Marin, 232, Puerto Rico, 10, heavyweights; Simon Brown, 150, Germantown, Md., knocked out Ozzie O'Neal, 148, Youngstown, Ohio, at 1:58 of the first round, welterweights; Lonnie Smith, 142, Denver, knocked out Eduardo Valdez, 149, Columbia, at 2:36 of the second round, junior welterweights.

COPENHAGEN, Denmark (AP) - Magne Havnaa, Norway, outpointed Daniel Netto, Argentina, 12, to retain the WBO cruiserweight title.

FERRARA, Italy (AP) - Massimiliano Duran, 186 1/2 , Italy, retained the WBC cruiserweight title when Anaclet Wamba, 189, France, was disqualified for butting in the 12th round.

SCOTTSDALE, Ariz. (AP) - Michael Carbajal, Phoenix, stopped Leon Salazar, Panama, at :45 of the fourth round to retain the IBF light-flyweight title; Robert Wangila, Kenya, stopped Verdell Smith, Memphis, Tenn., 3, TKO, welterweights; Scotty Olson, Canada, stopped Esteban Rodriguez, Phoenix, 3, TKO, flyweights.