How many World Champions won and lost their titles in the opening round? without looking it up I can think of two.
Young Corbett (he had a number after his name which I forget) who lost to Jimmy McLarnin in the earlt thirties. Art Frias who lost by tko in 1 to Boom Boom Mancini. Edwin Rosario lost one of his alphabet soup titles back in the late eighties to someone by 1 round tko (he wasn't decked however) Bruce Seldon lost a 'title" to Mike Tyson in the early ninties in 1. Let's not forget "Terrible Tim" Witherspoon who lost in1 to Bonecrusher Smith.
I forgot Pone Kingpetch of Thailand who lost the flyweight title to a Japanese fighter in the early sixties.
George Chip lost his title in one round to Al McCoy. This unfortunately overshadows the fact that Chip was a great fighter.