LAS VEGAS — If the Baltimore Ravens are to become Super Bowl champions, they’ll have to beat the odds again to do it.

Bookmakers in this gambling city mostly have the San Francisco 49ers 4.5-point favourites over the Ravens in the Super Bowl, amid expectations this could be the heaviest bet title game ever.

"It’s a monster matchup, brother versus brother," William Hill oddsmaker Jimmy Vaccaro said. "I believe it will top last year’s Super Bowl handle and could go higher."

Some sports books didn’t even wait until the clock ran out in the Ravens 28-13 win over the New England Patriots to set the line. At the LVH sports book, a line favouring the 49ers by 4.5 points was put up just before the 2-minute warning, and bettors didn’t waste any time to get money down on the game.

"We’ve got money coming in as we speak, it looks like it will be good on both sides," said LVH book director Jay Kornegay. "These teams mirror each other, but the 49ers are a bit more sexy now than the Ravens."

At William Hill, which operates 75 betting parlours in Nevada, oddsmakers opened the game with the 49ers a 5-point favourite, as did some other books. But it was quickly bet down to 4.5 points, a line that seemed to be holding in the early betting.

"We had what I consider a large bet come in at 5 points and moved down from there," said Vaccaro, who said he believes the line will hold between 4 and 4 1/2 points until close to the day of the game.

Baltimore already is the first underdog of more than a touchdown to win both the division and championship playoff rounds. The Ravens were 7.5-point underdogs to the Patriots before beating them to win Sunday's AFC title game.

"The Ravens are the hot team now but they’re not getting a lot of support from the public," Kornegay said. "These are very similar teams, both can run the ball well, play smash mouth football and have two quarterbacks playing very good football."

Last year’s game between the New York Giants and the Patriots drew $93.9 million in wagers in Nevada, just under the record $94.5 million bet in 2006 when the Pittsburgh Steelers beat the Seattle Seahawks 21-10. Those who follow the betting industry closely say hundreds of millions of dollars — possibly even billions — will be bet on the game by the time the offshore sports books and illegal bookmakers take in their share.

Like the LVH, some books in Las Vegas opened the game at 4.5 points, while others put their number up at 5. Most of the major Las Vegas sports books were at 4.5 points, with a few listing the 49ers at 4 points Sunday night.

The over/under, where bettors can wager on whether the two teams will combine for more or less points than the posted number, was at 49 points at most books.

Point spreads fluctuate on games, especially the most heavily bet ones, according to how much oddsmakers take on each team. A big bet on one team can sometimes send a line moving a half point one way or another, though most movement normally takes place in the days just before the game.

Nevada oddsmakers also post hundreds of proposition bets on the game, everything from who will win the coin flip to which quarterback will have more passing yards. Those bets aren’t expected to be posted fully until later in the week.

Vaccaro said the proximity of the 49ers to Nevada should boost betting on the game.

Casinos have lost once only once on the Super Bowl the last 10 years, in 2008 when bettors gambled $92 million and casinos lost $2.57 million as the Giants beat New England, 17-14.