Australian tennis star Ashleigh Barty has fallen a win short of crowning her triumphant grand slam season with a second straight US Open doubles title.

Barty and Victoria Azarenka lost 7-5 7-5 to third seeds Aryna Sabalenka and Elise Mertens in Sunday’s final in New York.

Australia’s French Open champion had been bidding to become the first player to claim back-to-back women’s doubles titles at Flushing Meadows in 12 years.

But the 23-year-old can instead console herself in the knowledge she’ll regain the world No.1 singles ranking on Monday after being unable to convert their clear dominance into victory over Sabalenka and Mertens.

Barty and Azarenka, both singles grand slam champions, blew a 3-1 lead in the first set and then twice dropped serve from 40-15 up in the second.

They especially rued not being able to convert any of four break points after Mertens was trailing love-40 on serve at 3-4 in the eighth game of the second set.

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“A few games we lost from 40-15 up, a couple of missed opportunities with volleys. There’s probably half a dozen points, maybe even less, that would turn a match,” Barty said.

“But they’re the what-ifs that we can’t worry about and can’t stress about. I think we still have to celebrate the fact that we’ve had a hell of a tournament.”

Despite the defeat, Barty remains in strong contention to become the first player to qualify for both the singles and doubles at the WTA’s season-ending championships in China since Karolina Pliskova in 2016.

Barty is the only player to have secured her entry in singles and is now in ninth spot with Azarenka in the Race to Shenzhen, which features the top eight doubles pairings of the year.

Australia’s French Open champion had been bidding to become the first player to claim back-to-back women’s doubles title in at Flushing Meadows in 12 years, but can instead console herself in the knowledge she’ll regain the world No.1 singles ranking on Monday.

Success over her fellow Belarusian Aryna Sabalenka and Elise Mertens would have been no less significant for Azarenka.

A two-times singles runner-up to Serena Williams at Flushing Meadows, as well as a dual Australian Open champion, Azarenka placed her career on hold to secure shared custody of Leo after a bitter legal battle played out in the Californian courts.

The two-year-old is with Azarenka as one of the tour’s most popular players strives to become tennis’s latest grand slam-winning super-mum.

“I always want to do well for my son and I hope he’s going to watch and see. He he did watch our quarter-finals match in the nursery here,” Azarenka told AAP.

“He doesn’t understand exactly what I do, which is cool, but we’ll see. Sunday is in two days and we’ll do my best.”

Seventh on the all-time women’s prize money list – behind only Serena and Venus Williams, Maria Sharapova, Caroline Wozniacki, Simona Halep and Petra Kvitova – with on-court earnings of $US30,104,670, ($A44.05m) Azarenka’s place in the Hall of Fame is already secure.

But the 30-year-old still yearns to fill a glaring omission on her glittering career CV.

“I haven’t had a title in doubles yet, a grand slam title,” Azarenka said.

“This whole two weeks I’ve been having a lot of fun on the court and I feel like every match we’re getting better and better.

“You can’t ever underestimate being in a grand slam final. I think as a tennis player, that’s what you dream of.

“If it’s singles, of course it’s always a priority, but being a doubles partner is always extra special so I feel very lucky to do that.”

Barty won the title last year with Coco Vandeweghe, but linked with Azarenka in 2019 due to the American’s battle with an ankle injury.

Back-to-back doubles triumphs to emulate Frenchwoman Nathalie Dechy in 2006-07 would cap a stellar grand slam season for Barty, in which the 23-year-old won the French Open and bettered or equalled career bests at all other three.

It would also be the perfect celebration of her impending return on Monday to the top of the world singles rankings.

“I feel like I’m in a great place off the court and enjoying myself on the court.” Barty said.