• Ash Barty's 2019 campaign could end with the Australian ranked world No.1 (Getty Images)Source: Getty Images
Ash Barty has regained the world No. 1 ranking and is favourite to become the first Australian to hold top spot at season's end.

Ashleigh Barty is poised to crown her phenomenal season by becoming the first Australian woman to top the year-ending tennis rankings.

Barty will officially regain the world No.1 spot on Monday after Naomi Osaka's fourth-round US Open loss to Belinda Bencic.

And the 23-year-old French Open champion is a hot favourite to finish 2019 at the summit having not only built a healthy rankings lead over her rivals but also having significantly fewer points to defend over the last two months of the season.

Realistically, only Karolina Pliskova can catch Barty but it will take a huge effort from the Czech to do so.

Barty will enter the Asian swing with a 376-point lead over Pliskova and with 372 rankings points less to defend.

Osaka will slip to No.3 in the world after the US Open and will trail Barty by 1655 points with 45 more points to defend.

That leaves Japan's reigning Australian Open champion with less than no hope of ending the season as No.1 for the first time.

Barty held the top spot for six weeks after clinching her third title of the season in Birmingham the week before Wimbledon, amid a 15-match winning streak highlighted by her grand slam breakthrough in Paris.

Evonne Goolagong Cawley is the only other Australian woman to have the No.1 ranking, for two weeks in 1976.

Barty said "it would be incredible" to join Lleyton Hewitt (2001 and 2002) as only the second Aussie to enjoy the year-end top status since women's rankings were introduced in 1975 and the men's in 1973.

"I don't know what I would need to do to get there. I haven't really sat down and done the maths or anything like that," Barty said in New York.

"But I have had my schedule planned for the last part of the year for the last few months, so that certainly won't change."

Barty's climb to the summit has been built on class and consistency.

The Queenslander has won an equal-tour-best 45 matches in 2019 and lost only eight times in almost 11 months.

Osaka, 21, lost her grip on top spot with a 7-5 6-4 loss to Swiss Belinda Bencic on Monday.

The defeat marked the end of a 17-match winning streak at hardcourt majors.

While Barty and Osaka each won one slam this year, the Japenese suffered a third-round exit at Roland Garros and was ousted from Wimbledon in round one.

As well as her French Open triumph, Barty was a quarter-finalist in Melbourne and reached the fourth round at both Wimbledon and Flushing Meadows.

The Queenslander celebrated her impending return to No.1 by storming into the US Open doubles quarter-finals with Victoria Azarenka.

Barty, the title winner last year with Coco Vandeweghe, and Azarenka brought teenage sensation Coco Gauff and fellow American prodigy Caty McNally crashing back to earth with a 6-0 6-1 mauling on Monday.

The 47-minute mismatch ruthlessly exposed the gulf between the pair of grand slam singles champions and world No.1s and the next-generation wannabes.

Barty and Azarenka will meet top seeds Timea Babos and Kristina Mladenovic for a semi-final berth.