Sportsbooks are facing their second straight Stanley Cup sweat.

Last year, as the expansion Vegas Golden Knights reached the Stanley Cup Final, Nevada bookmakers found themselves rooting against the hometown squad to avoid a multi-seven-figure loss. This year, they're sweating the upstart St. Louis Blues, who have authored one of the greatest in-season turnarounds in recent memory, going from 300-1 longshots in January to Stanley Cup finalists in May.

"We're actually worse [on the Blues] than what the Knights would have been," Bill Sattler, director of specialty games for Caesars Entertainment, said, adding that a St. Louis victory over the Boston Bruins in the Stanley Cup Final would cost the sportsbook a net loss of "mid-six figures" on their odds to win the Stanley Cup.

Bookmakers escaped when the Knights lost to the Washington Capitals in last year's Stanley Cup Final and are hoping for another Boston title this year.

The Bruins are around -150 favorites to win their Stanley Cup Final series, which begins Monday. Halfway through the season, few people thought they'd be facing the Blues.

Entering the season, St. Louis was considered a second-tier Cup contender, with odds around 25-1. The Blues got off to a slow start, though, made an early coaching change and in December were listed among the biggest longshots on the board. On Dec. 17, only the Chicago Blackhawks, who were 10-19-6 at the time, had worse odds to win the Stanley Cup than St. Louis.

There were a few believers willing to stake a few dollars on the Blues at that point, but not many. The SuperBook at Westgate Las Vegas said it took just one bet -- a $20 wager on Dec. 28 -- on the Blues at 300-1. New Jersey sportsbook PointsBet said it didn't take its first bet on St. Louis to win the Stanley Cup until Feb. 20.

The largest bet Caesars took on the Blues at 250-1 was $400, but Sattler said there were several more in the $100 range. With odds in the triple digits, it doesn't take much to build up some hefty liability.

"We had them at 250-to-1 halfway through the season," Sattler, a 40-year-plus Vegas veteran, said. "A few hundred-dollar bets here and there, and it gets up there."

Few teams have overcome such long odds midway through a season and gone on to win a championship in one of the four major U.S. leagues. One of the most recent examples also hails from St. Louis. The 2011 St. Louis Cardinals were listed at 999-1 in September when they were five games out of the wild card with 15 games to play. They rallied to make the playoffs and went on to beat the Texas Rangers in the World Series.

The 1999 St. Louis Rams began the season as 300-1 longshots, but behind quarterback Kurt Warner, they quickly showed they were legitimate championship contenders. The Blues, however, weren't even in the playoff picture midway through the season.

Bolstered by the emergence of goalie Jordan Binnington, the Blues began to improve during the second half of the season, and a few more bets began to trickle in on St. Louis. A customer at the FanDuel sportsbook at the Meadowlands put $2,700 on the Blues at 21-1, and William Hill's books reported taking four $2,000 bets on St. Louis to win the Cup in mid-February.

However, entering the playoffs, 10 of the 16 teams alive in the postseason had attracted more bets to win the Stanley Cup than the Blues at William Hill. Caesars Sportsbook went into the postseason with a liability on only four teams to win the Stanley Cup. The Blues were the only ones who made the playoffs.

"You want people to bet the 250-to-1 longshots," Sattler said. "You just don't want those teams to go from last place to the Stanley Cup."