The return of the NFL and the Denver Broncos, as well as a multitude of new operators making their debuts, saw Colorado return its biggest month of sports betting to-date.

September’s handle, which was released on Friday by the Colorado Department of Revenue’s Division of Gaming, was up 61 per cent from $128.6m in August. September’s wagers led to $4.2m in gross gaming revenue, down 45 per cent from $7.5m in August.

This saw Colorado edge Indiana to temporarily take over the number four spot among US legal sports betting markets. Indiana also enjoyed a record September with $207.5m in handle. Fledgling Illinois, which leapfrogged the Centennial State with $140m in August bets, has yet to announce its September data.

September’s gains netted a loss of $3.4m in betting proceeds, down from $1.9m in August, a product of bad luck and heavy promotions for the state’s sportsbooks. Despite the loss, $69,772 was injected into state coffers.

“Colorado is nowhere near maturity as a market, and yet its gains continue to put it among the top markets in the US,” said Dustin Gouker, lead analyst for PlayColorado.com

“Interest in the Denver Broncos was bound to help spur interest in the NFL’s first few weeks. But September still managed to outpace what we could have reasonably expected just two months ago.”

Online sportsbooks have proven to be by far the overwhelming preference for Colorado’s bettors, with $203.9m, or 98.2 per cent, of all of the wagers being made online. No other major legal sports betting market has seen such a high percentage of its monthly handle generated online.

In September alone, Colorado welcomed the launch of four new online sportsbooks, including theScore, William Hill, Betfred, and Sportsbetting.com.

“The Colorado market will continue to sort itself out for the foreseeable future, and its growth prospects remain enormous as more and more operators enter,” added Jessica Welman, analyst for PlayColorado.com.

“Illinois’ population will make it nearly impossible for Colorado to keep pace, but catching Indiana so quickly is impressive. In fact, Colorado’s race with Indiana remains among the most intriguing storylines of US sports betting.”