NEW YORK (Reuters) - The start of the National Football League season brought a rush of online betting for sports wagering provider DraftKings, where total bets in a single day equaled 10 percent of the number of bets placed over the previous five weeks, the company said.

FILE PHOTO: People wait in line to place bets after Super Bowl XLVIII proposition bets were posted at the Las Vegas Hotel & Casino Superbook in Las Vegas, Nevada January 23, 2014. REUTERS/Las Vegas Sun/Steve Marcus/File Photo

It took DraftKings, which operates mainly as a fantasy sports company, 38 days to reach one million sports bets since launching its online sportsbook in New Jersey on August 1, company co-founder and Chief Revenue Officer Matthew Kalish told Reuters in a telephone interview on Tuesday.

During Sunday’s season-opening games more than 100,000 bets were placed through the sportsbook.

“It was a massive spike from what we were seeing in August,” Kalish said. “We absolutely hit our expectations.”

Over the weekend, 51 percent of DraftKings sportsbetting customers placed bets versus roughly 35 percent for most days in August. About 90 percent of DraftKings wagerers have returned to bet again, Kalish said.

The bump in volume and high retention rate signals a strong professional football season ahead for DraftKings’ sports betting, Kalish said. “It shows a lot of positivity going into the NFL season,” he added.

New Jersey is one of a handful of states that have rolled out full-scale sports betting programs since a U.S. Supreme Court decision on May 14 lifted a federal ban on sports wagering. It is the only state to have launched comprehensive online sports gambling since the ruling.

DraftKings was not alone in seeing a bump in wagers as the NFL season got underway, but data was limited.

SugarHouse Online Sportsbook, which has accepted online bets in New Jersey for less than three weeks, saw wagering volume roughly double during the first weekend of the NFL season versus the prior weekend, said Mattias Stetz Chief Operating Officer of Rush Street Interactive, which runs SugarHouse.

Sunday night’s exciting come-from-behind win by the Green Bay Packers over the Chicago Bears drew the most wagers so far because it attracted a large number of live betting, when bets can be paced on every drive, Stetz said.

“When you don’t really know who’s going to win, that makes it more interesting for people to bet,” he said.

In Mississippi, which has only approved sports betting at brick and mortar casinos, the Beau Rivage Resort and Casino took in 2,000 more bets on Sunday compared with the day before, Beau Rivage sportsbook manager Will Hall said on Wednesday.

“The whole casino was buzzing,” Hall said.