NFL underdogs went on a run Sunday that produced a significant transfer of wealth in Las Vegas.

Ten of Sunday's 13 underdogs covered the spread, with six teams pulling outright upsets. For some bookmakers, it was their most lucrative NFL Sunday ever. For the betting public, it was a multimillion-dollar defeat.

On an average NFL Sunday, sportsbook operator CG Technology will win 4-6 percent of the amount wagered. This Sunday, CG Technology kept more than 16 percent of the money bet on the NFL at their sportsbooks, according to vice president of risk Jason Simbal.

"It was certainly one of the best days we've had," Simbal told ESPN on Sunday night.

All the big decisions went the books' way. Upset wins by the Buffalo Bills and Chicago Bears, combined with the Houston Texans covering the spread against the New England Patriots, ended the bulk of parlay bets early in the day.

The Denver Broncos, who lost at Buffalo, were included on more parlay bets than any other team at Caesars Palace sportsbooks.

The Bears' overtime win over the Pittsburgh Steelers set the tone at MGM, which took a $340,000-plus money-line bet on the Steelers to win straight-up at -340 odds. That money stayed with the book.

"We had a ton of money-line parlays on the Steelers, ton of teasers," Jay Rood, vice president of MGM race and sports, said. "That was a complete blow to the public."

The biggest win of the day for the books, though, came at night when Washington, a 3-point underdog, ran over the Oakland Raiders in a 27-10 win. An hour before kickoff at MGM's sportsbook, seven times as much money had been bet on Oakland as had been bet on Washington.

William Hill, Nevada's largest sportsbook, reported a record Sunday, and most books said it ranked right up there with their most lucrative Sundays ever.

"It was as good as one Mayweather-McGregor fight," Frank Kunovic, director of specialty games for Caesars Entertainment, added.

Sportsbooks won millions of dollars on Floyd Mayweather's knockout of Conor McGregor in late August.

Heading into the Monday night game, underdogs were 11-3 against the spread, including the San Francisco 49ers covering as 3-point underdogs in a 41-39 loss to the Los Angeles Rams on Thursday. The Arizona Cardinals are 3-point underdogs to the Dallas Cowboys on Monday.

The Minnesota Vikings could have been the 12th underdog to cover the spread on Sunday. The Vikings were underdogs to the Tampa Bay Buccaneers for most of the week, before late sharp money showed up on Minnesota to drive the line down to pick 'em when the game kicked off. The Vikings won 34-17.

Sunday's windfall for the books could have been even bigger, but multiple operators reported that handle on the NFL was down slightly.

"Our handle was down a little bit, but not significantly," John Avello, executive director for Wynn race and sports, said. "I'm certainly not complaining."

The NFL parlay lottery in Delaware also experienced a boon from the Sunday underdogs. According to executive director Vernon Kirk, $2.9 million was wagered on Sunday, with the lottery winning $2.4 million of it.