Samantha Stosur's US Open title defence is over after the Australian suffered a heartbreaking three-set loss to world No.1 Victoria Azarenka in a high-octane quarter-final at Flushing Meadows.

Stosur won her first set against Azarenka in six career encounters, but still came up painfully short as the Belarusian prevailed 6-1 4-6 7-6 (7-5) in a thrilling contest lasting almost two-and-a-half hours.

Azarenka will face either third-seeded French Open champion Maria Sharapova or 11th-seeded Frenchwoman Marion Bartoli for a spot in Saturday's title match.

Stosur was so close, conjuring a mini match point in the 11th game of the deciding set, but Azarenka saved it with a big ace down the middle before clinching an epic victory in the tiebreaker.


"I have no words. You could feel the pressure," Azarenka said.

"We played some great tennis. The level was so high. We both gave it our all.

"I think she played amazing. She made me play my best tennis. She kept hitting the lines."

That Stosur even managed to make a contest of Tuesday's quarter-final after Azarenka steamrolled her in the first set was amazing.

Early on, Stosur had no answer to the Australian Open champion's awesome firepower and control.

Stosur made a dire start, broken to love inside a minute in the opening game of the match with four unforced errors.

She then dropped her second service game to fall behind 3-0 before taking shelter during a 90-minute rain delay.

Upon the resumption, Azarenka rolled through the first set, taking it in precisely half an hour to be seemingly in complete control.

Just winning a rally, a point, was a struggle as Azarenka dictated from inside the baseline.

Stosur, though, first showed signs of life when she upped the ante to break Azarenka in the opening game of the second set as the Belarusian tightened up with two double-faults.

The Australian had every right to raise the white flag after playing a great service game only to be broken back for 1-1.

But she dug in as the tempo of the match raised significantly with both players producing some incredible tennis.

With Stosur pressing to the limit, her only hope seemed to be if Azarenka - a player prone to the odd meltdown - faltered.

That's exactly what initially transpired.

Feeling the strain, Azarenka double-faulted again and then was unable to control a wide-angled forehand from Stosur as the titleholder's grit went rewarded with another decisive break in the seventh game.

Stosur held her nerve and serve from 15-30 to close out the set - that in itself a milestone - and force a decider.

Stosur dropped serve from 30-0 up in the fourth game to trail 3-1, only to step up and break back the very next game.

But she looked in deep trouble when the top seed jumped to a 4-2, 40-15 advantage with her sixth service break.

Stosur refused to go away, inducing an Azarenka racquet-smashing dummy spit with her extraordinary scrambling to get back to deuce.

Stosur then rifled an off-forehand return winner not dissimilar to the one she delivered on match point against Serena Williams in last years's final to get back on serve.

Almost inevitably given the quality and evenness of the pair, the quarter-final was decided in a breaker.

It looked all over when Azarenka charged to a 4-0 advantage.

But Stosur rallied and had the chance on serve at 5-5 to move to match point.

However, a forehand from the Australian caught the net tape, allowing Azarenka to pounce and then seal victory when Stosur couldn't control a forehand on match point.