Filipino boxing superstar Manny Pacquiao started fight week as the betting underdog against WBA welterweight champion Keith Thurman, but a flood of money has seen ‘Pac-Man’ become the fight-day favorite.

Pacquiao (61-7-2, 39 KOs) takes on undefeated world champion Thurman (29-0, 22 KOs) at the MGM Grand Garden Arena in Las Vegas as the Filipino legend bids to claim the 13th world title of his stellar career.

And while the 40-year-old may be a decade older than his world champion opponent, that fact hasn't stopped fans declaring their allegiance for the former eight-division world champ.

When betting for the fight first opened in Vegas, Pacquiao was installed as the pre-fight underdog, but as fight week progressed, Vegas punters and professional gamblers alike flocked to the big casino sportsbooks and laid down their money as the betting momentum drastically shifted from the defending champion to Pacquiao.

"It's just been nothing but Pacquiao money," Westgate sportsbook director John Murray told the Las Vegas Review Journal.

"No matter what we make the price, Pacquiao is the only side anyone wants to bet. We had a guy come in (Friday) morning who bet Pacquiao for $5,000 at -165, so we went up to -170.

"We've taken some money on Keith, but it's been a pretty one-sided fight so far."

It's been a similar story further down the strip at Caesars, with their sportsbook's risk manager Jeff Davis telling the Review Journal: "We're going to need Thurman for a ton.

"We've taken a slew of Pacquiao money, and all the money the night of the fight will be on Pacquiao."

PACQUIAO AND THURMAN: FACE TO FACE