Novak Djokovic confirmed his status as the world’s premier tennis player with a thrilling victory over Roger Federer in Sunday’s U.S. Open final, but the 28-year-old has a long way to go if he wants to surpass Federer as the sport’s endorsement king. Federer has nearly doubled Djokovic’s take from off-court endeavors over the past year, despite clear and repeated evidence that Djokovic is now the stronger player.

With his win at the U.S. Open, Djokovic secured his third grand slam title of 2015 and cemented his world No. 1 ranking for the fourth time in five years. The gangly Serb earned $17.2 million in tournament prize money from June 2014 to June 2015, more than any other tennis player. Yet Federer, 34, rode endorsement deals with premium brands like Nike and Rolex to $58 million in off-court earnings over that same period; Djokovic, who focused on deals with smaller companies, brought in $31 million, according to Forbes. But as Federer’s career begins to wind down, experts say Djokovic is well-positioned to take his place as the sport’s top ambassador.

“I think his window is coming now. Last night opened another opportunity for him,” said Joe Favorito, a longtime sports marketing professional and instructor at Columbia University in New York City. “It’s up to him and his management team to decide if this is where they want to go and spend more time doing things off the court versus on the court.”

Federer’s place as tennis’ leading brand ambassador is well-earned. He’s on the short list of the greatest players in tennis history, with a record 17 grand slam titles and nearly $100 million in career prize money. With more than a decade of on-court dominance and a jovial personality that exudes calm in pressure-packed moments, Federer is still a fan favorite, even as his on-court skills have waned.

Djokovic is younger than Federer but he already has put together a lengthy list of accomplishments. He has been the world’s top-ranked player for the past several years and he has amassed 10 grand slam title wins, including victories at this year’s Australian Open, Wimbledon and now the U.S. Open.

While Djokovic has demonstrated plenty of on-court personality – notably through his hilarious impressions of fellow players, including Maria Sharapova – Djokovic traditionally has shown a bit more on-court emotion, even anger, than Federer. Djokovic issued public apologies twice this year for yelling at courtside attendants, once at the Miami Open and another time at Wimbledon. On the latter occasion, he made a ball girl cry. In terms of popularity with fans, there’s no question that Federer has the edge.

That distinction was clear at in New York’s Arthur Ashe Stadium on Sunday, when fans repeatedly cheered Federer’s points while celebrating Djokovic’s failures. Djokovic acknowledged the difference in support at his post-victory press conference.

“I can’t sit here and criticize the crowd,” Djokovic said, according to ESPN. “On the contrary, I think it’s logical to expect that a great player and a champion like Roger has the majority of the support anywhere I play him. I accept that fact.”

Market research supports the notion that audiences – and brands – favor Federer over Djokovic. The Marketing Arm, an international marketing and promotion agency that specializes in sports and entertainment, compiles the “Celebrity DBI,” an index that conducts surveys of hundreds of consumers nationwide and ranks a celebrity’s marketability based on the results.

More than 60 percent of U.S. consumers are aware of Federer, meaning the Swiss player has a marketing reach similar to that of hip-hop megastar Drake or “Family Guy” creator Seth MacFarlane. Federer also has a 73 percent likability rating, and he’s ranked alongside actor Channing Tatum among celebrities that Americans most aspire to imitate.

Djokovic has far less reach -- less than 30 percent of U.S. consumers know him by name, according to Marketing Arm data. Djokovic’s rankings on likability, consumer trust and overall influence were far lower than Federer’s.

“Novak is a little more – I don’t like to use the word brash, because it has a negative connotation – but he yells on the court, he shows a lot more emotion,” said Matt Delzell, the Marketing Arm’s managing director. “That sort of personality can turn some folks off, and again, I think that’s reflected in the numbers.”

Federer has parlayed the support he enjoys from American fans into several massive, high-profile endorsement deals. Aside from his exclusive, personalized line of Nike apparel, Federer has agreements with premium brands like Rolex watches and Mercedes-Benz vehicles.

“Roger Federer, to take the late [ESPN personality] Stu Scott’s term, is as cool as the other side of the pillow. He speaks five different languages. On the court, he doesn’t even look like he’s sweating, no matter who he’s playing,” Delzell said.

It's difficult to question the marketing strategy of an athlete who pulled in $31 million in endorsements in the past 12 months, but Djokovic is less aggressive than Federer at ingratiating himself to American consumers. He has deals with the Australia and New Zealand Banking Group, Australian wine brand Jacob’s Creek, French car brand Peugeot and Japanese clothing retailer Uniqlo. None of those brands are particularly visible in the U.S. marketplace, particularly when compared to household names like Nike or Rolex.

It could be a personal choice. Endorsement campaigns can be time-consuming, and Djokovic, whose workout regimen has become the stuff as legend, may prefer to focus mostly on tennis. It’s also possible that tennis’ location on the periphery of the American sports landscape has limited his opportunities.

“I think there’s only room for a few tennis players to capture the lion’s share. Marketers look to distribute their sports sponsorships across sports,” said Allen Adamson, North America chairman at Landor Associates, a marketing firm. “Tennis is a bit of a niche sport. It doesn’t have the broad-base appeal of a basketball or a football or even golf, to a certain extent.”

But as Federer nears retirement, and fellow tennis titan Rafael Nadal battles the injuries that have derailed his career in recent months, Djokovic is in prime position to take over Federer’s spot. He just has to have the will to do it.

“The American public has loved Roger Federer for a long time,” Favorito said. “They’re just learning how to love Novak Djokovic.”