• Barstool Sports founder Dave Portnoy bet $600,000 on UConn to win the NCAA men's championship.
• He won $2.7 million.
• DraftKings reported a record NCAA tournament, with sports betting now legal in 38 states plus Washington, D.C.

Barstool Sports founder Dave Portnoy is cashing in $2.76 million on UConn's big win over Purdue on Monday night in the NCAA men's championship game.

Portnoy tweeted the massive score off a March 20 $600,000 wager on the Huskies winning the national championship. Portnoy's bet was a moneyline wager placed right before the NCAA tournament began, and required UConn to win six straight games for it to pay off for him. The bet paid off at 3.6-to-1.

DraftKings confirmed to CNBC it took the bet.

"The greatest bet of my life," Portnoy said in the post on social media site X. "The biggest win of my life by a mile."

Barstool signed a multiyear deal with DraftKings in February. The sports media company was previously owned by Penn Entertainment.

DraftKings reported a record NCAA tournament, with sports betting now legal in 38 states plus Washington, D.C. — five additional states since this time last year.

The American Gaming Association estimated Americans would legally wager $2.72 billion on the March Madness tournaments this year. That's equivalent to 2.2% of the total handle wagered on any sporting events last year.

Geolocation tracking company GeoComply, which operators use to police bettors' locations, told CNBC it saw a 42% increase in checks over the 2023 tournament.

DraftKings said Monday's game was the most bet-on college basketball game of all time for the sportsbook.

FanDuel said the men's championship game saw a 52% year-over-year increase in bet count and a 42% year-over-year increase in handle.

At Caesars Sportsbook, Monday's championship game accounted for the most same-game parlays ever placed on a college basketball game.

"It was a tournament for the customers as favorites covered the spread 61% of the time," Craig Mucklow, Caesars Sportsbook's vice president of trading, said in an email.

Betting on the women's tournament was particularly lucrative for the sportsbooks.

South Carolina's undefeated season and the heroics of superstar Caitlin Clark fueled a massive influx of bets. FanDuel, BetMGM and Fanatics say the championship game was their single biggest betting event on women's sports. Caesars said the women's championship saw double the previous handle record for a women's college basketball game.

"We could only imagine the handle if the game was given a proper primetime slot," Mucklow said of the women's final.

— CNBC's Dan Mangan contributed to this report.