Michael Spinks knocked down challenger Johnny Davis in the eighth round before stopping him in the ninth yesterday to retain his World Boxing Association light heavyweight title for the fifth time.

Referee Larry Hazzard halted the scheduled 15-round bout in Atlantic City, N.J., at 2:27 of the ninth after Spinks landed a straight right punch to Davis' chin.

Davis, shielded by his cornermen, was in tears as he walked from the ring. Blood was trickling from cuts over his swollen left eye and lower lip.

Davis opened aggressively, forcing Spinks to the ropes, and had the edge in punches through the first three rounds. But after the fourth round, he lost his punching power and began clutching at the champion.

Spinks landed punches almost at will in the eighth round as the challenger tried desperately to cover up. Spinks, who won the title from Eddie Mustafa Muhammad 14 month ago, sent Davis to the canvas with a right chop to the ear, but the challenger beat the count just before the bell sounded.

With this bout, the champion from St. Louis tied Bob Foster's record of four title defenses within a single year. The victory took Spinks a step closer to a showdown later this year with World Boxing Council champion Dwight Braxton, who was ringside for this one.