When Juan Manuel Márquez challenges undefeated Timothy Bradley for the WBO welterweight championship Saturday in Las Vegas, the reverberations will be felt in Mexico, where the love of the bruising art is deep and being a champion means something more than making millions.

Boxing is the second-most popular sport in Mexico, after soccer. This was evident on Sept. 14, when Mexican Saul "Canelo" Alvarez lost a majority decision to Floyd Mayweather Jr.—and nearly eight of 10 households in Mexico with televisions tuned...