The world’s largest online betting company suffered a run of “very unfavorable” US sports results at the end of the year with the highest rate of favourites winning in nearly 20 years.

Flutter Entertainment, once known as Paddy Power Betfair and now behind betting brands including FanDuel and Sportsbet, said on Tuesday night that the “customer friendly” results generated an estimated adverse gross gaming revenue impact of $438 million, and estimated reductions in revenue of approximately $390 million between November 12 and the end of December.

The biggest single loss during the quarter was from an American football game on the second last day of the year when the Detroit Lions’ thrilling win over the San Francisco 49ers which cost the business $74