Both guys were chinny, but Uncle Roger was the more technically sound fighter, with a monster right hand. Plus, his chin was more sturdy (i.e. less bad) at 140. Roger gets stunned or hurt and then comes back to stop Khan.
Roger Mayweather knocks him out, Mayweather SR knocks him out, Mayweather Jr knocks him out and Jeff Mayweather knocks him out but he knocks Garcia SR out at least.