Guts Ishimatsu was a very tough fighter, he won the WBC World Lightweight Title by Kayoing Rodolfo Gonzalez on April 11 1974, TKO 8. This after his unsuccessful bid against WBA Lightweight Champion Roberto Duran on Sept 8 1973, TKO 10. He did repeat another win over Gonzalez, and also defeated former champion Ken Buchanan on Feb 27 1975, by unanimous decision. He was a very tough body puncher, Duran once remarked that Guts hurt him to the body, when they fought with a hard body shot. Ray Boom Boom Mancini was stopped by WBC Lightweight Champion Alexis Arguello in round 14, on Oct 3 1981. He won the WBA Title by stopping Art Frias on May 8 1982, TKO 1, and defended against Deuk Koo Kim on Nov 13 1982, in a nationally televised title bout. After a furious battle in this scheduled 15 rounder, after being struck by Mancini in round 14, Kim collapsed, after being knocked down, later he passed away. It did affect Ray emotionally. Ray stopped Bobby Chacon on Jan 14 1984, in round 3, before losing his title to Livingston Bramble on June 1 1984, TKO 14. This bout would feature two body punchers, both very aggressive fighters, Guts, the more experienced should win this bout, TKO 10, after suffering a knockdown, in round 5.
I’m going to go with Mancini. Guts certainly had a run there for a while with two wins over Gonzalez and a likely-slightly-past-it Buchanan, but he also lost a ton of fights at the domestic level and most of his step-up fights before this. Mancini had a warrior’s heart and let’s not forget he ran Jose Luis Ramirez out of the ring. Also Kid Dynamita Morales and also quality wins over Ernesto Espana (who kept turning up like a bad penny at 135 in this time span) and Orlando Romero. The Arguello loss was to a prime ATG sharpshooter and Boom Boom was able to hang pretty well and learned from that fight. It made him better. I think Ray shows his own guts and out-hustles Guts for a close win over 15 in a action fight.
