Walker said the largest wager on De La Hoya was $90,000, as of two hours before the fight. Most of the small wagers were on De La Hoya at plus-150, but it's normal for the underdog to attract more action.

"That's not to disparage Mayweather," Walker said. "Every big fight at the MGM or Mandalay Bay, we need the favorite to win."

Mayweather, who entered the fight 37-0, opened as a minus-230 favorite in November. But De La Hoya's popularity is unsurpassed in boxing.

"The action we're getting on the fight is unreal," Walker said. "It's really a megafight in every sense of the word, and I think people are betting accordingly. People who normally bet $100 are betting $1,000 this time."

The odds on De La Hoya to win by knockout dropped from 5-1 to 3-1, and the odds on it ending in a draw dropped from 12-1 to 8-1.

"If De La Hoya wins by knockout, we're in bad, bad shape," Walker said.