Ashleigh Barty’s US Open campaign is over, with Australia’s biggest women’s singles hope falling to former finalist Karolina Pliskova in the fourth round.

The eighth-seeded Czech showed her class in a 6-4 6-4 victory over Barty despite being under pressure for much of the match on Sunday.

Barty won just about everywhere but on the scoreboard, striking 29 winners to Pliskova’s 16, out-aceing the Czech six to four and offering up only two break points on serve.

Tellingly though, Barty was unable to capitalise on any of eight break-point chances, while Pliskova converted both her only two – one in each set, in the one-hour and 24-minute triumph.

“It’s disappointing because I know that wasn’t my best tennis today that I’ve played across the past month,” Barty said.

“But she did play the big points better today.”

Despite her exit, Barty’s breakout grand slam run ensures the 22-year-old a career-high ranking of No.15 in the world next week.

“It’s been really positive,” the Queenslander said after nine of her 12 matches over the American hard-court swing.

But while Pliskova was too clutch in the big moments, Barty paid dearly for her misfiring forehand on Sunday.

She dropped serve from 40-love up in the opening game of the match, wildly overhitting a forehand with an open court in offing while down a break point.

The errors continued to flow from her favoured wing as she dragged another forehand wide while having Pliskova down 15-40 in the eighth game.

With Barty unable to break back, Pliskova served out the first set to claim the upper hand.

Serving at 1-1 in the second set, Barty double-faulted to gift Pliskova a second break point, which the Czech converted with a vicious backhand crosscourt winner.

For all her pluck, there was no break back for Barty as the 2016 runner-up edged to within two wins of a second grand slam final appearance in New York.

Barty remains in the hunt for a maiden grand slam doubles crown with the four-times runner-up through to the third round with American partner Coco Vandeweghe.

“The best part is the tournament’s still going with Coco. That’s the beauty of doubles,” Barty said.

“We get to go out there tomorrow and have some fun and keep enjoying this amazing week that we’ve had, and the last month in particular as well.” 

The former Wimbledon junior champion lost all four major doubles finals with Casey Dellacqua before the West Australian retired earlier this year.

“I would have loved to have done it with Case. That’s always the thing we had hanging over our heads and our shoulders,” Barty said.

“But we’re still a very long way off that and hopefully we can get another win tomorrow.”

Pliskova will play Serena Williams in the US Open quarter-final. Photo: Getty

Elsewhere, Serena Williams was pushed in her fourth round clash with Kaia Kanepi, losing the first set to love before mounting a comeback to win, 0-6 6-4 6-3.

She will face Pliskova in the quarter-final on Wednesday.

Meanwhile, World No.1 Rafael Nadal has set up an intriguing quarter-final showdown with Dominic Thiem after snuffing out a comeback attempt by Georgia’s Nikoloz Basilashvili with a 6-3 6-3 6-7 (6-8) 6-4 win.

The top seed looked like he would cruise to an easy win on Sunday after pocketing the first two sets but the Georgian stepped up his game to take the third set.

The US Open champion would not be denied and fired his seventh ace on match point to end the three hour, 20-minute tussle.

-AAP