The Super Bowl is always the biggest sports betting day of the year. This year, the sports betting holiday comes to the gambling capital of the United States.

Las Vegas will be the site of Super Bowl LVIII, and there will be plenty of betting on a fun Super Bowl matchup.

The San Francisco 49ers were a 2-point favorite at BetMGM over the Kansas City Chiefs in the opening spread for the Super Bowl. That numbered settled to 1.5 on Sunday evening before going back to 2 on Tuesday. Meanwhile, the total was 47, though it moved to 47.5 shortly after it was posted.

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Point spreads and totals move often in the two weeks between the matchup being set and the game itself. The spread can move based on bets coming in on one side or a key news update such as an injury.

But to start, the 49ers are small favorites over Patrick Mahomes and the Chiefs.

49ers are favored to beat the Chiefs

The 49ers and Chiefs didn't meet this season. They last played in Week 7 of the 2022 season, right after the 49ers acquired Christian McCaffrey in a trade. The Chiefs were 1-point favorites and won 44-23. The 49ers fell to 3-4 with the loss, in which McCaffrey barely played. The 49ers have rarely lost since then.

While the 49ers and Chiefs were very good this season, neither team was great against the spread in the regular season. The 49ers were 9-8 against the spread and the Chiefs were 8-7-1, according to Action Network.

The Chiefs have been the more dominant team in the playoffs. They won comfortably against the Miami Dolphins, then beat the Buffalo Bills and Baltimore Ravens on the road. The 49ers trailed in the divisional round against the Green Bay Packers and in the NFC championship game against the Detroit Lions but came back to win both. The 49ers didn't cover the spread in either playoff win.

Despite the 49ers' close calls, the Chiefs' championship experience and Patrick Mahomes' playing better lately, the 49ers are favored to win the Super Bowl.

Super Bowl underdogs on a winning streak

In the past three Super Bowls, the underdog covered the spread. That underdog streak includes the Chiefs, who closed as a 1.5-point underdog in last season's Super Bowl against the Philadelphia Eagles and won straight up.

The Chiefs also lost as a favorite three years ago. They were a 3-point favorite against the Tampa Bay Buccaneers and lost 31-9.

Usually, the favorite wins the Super Bowl. Favorites are 37-19 straight up in the Super Bowl, according to Vegas Insider (Super Bowl XLIX between the Seattle Seahawks and New England Patriots was a pick 'em). Favorites are 28-26-3 against the spread, cutting the gap over the past three seasons.

The biggest underdog to win straight up came in Super Bowl III, when the New York Jets won as an 18-point underdog. It seems unlikely that record will be broken because it's unlikely we'll see another Super Bowl underdog of 18 or more points.

Unders had been on a streak before last season. In four Super Bowls in a row, the under hit. Last season, the Chiefs beat the Eagles 38-35, and the game went comfortably over the total of 51.5. There has been an even split on overs and unders in Super Bowls. There have been 28 overs and 28 unders; Super Bowl I didn't have a total according to Vegas Insider's history.