Can the former world number 31 back it up? On the evidence of the forehand winner, you'd suggest she can... great start from Tsvetana Pironkova. 30-0.

This time the Bulgarian gets it! A sliced forehand followed up by two furious backhands to break serve and take the advantage in this opening set.

Williams holds her forehead, looking to regain some composure. Not quite found her line yet and a long backhand hands Pirinkova another chance to break.

That's the response Serena Williams was after! An ace that was beyond her opponent before she could blink. Break point saved.

Double fault from Serena Williams. And that offers Pirinkova a first break point...

Barry Cowan
Former British tennis player on BBC Radio 5 Live Sports Extra

You've got to stay with Serena Williams as long as you can as there is a lot of expectation on her, the public have been waiting a long time for her to match Margaret Court's record. Pironkova is playing better than her purely in terms of ball-striking from the back.

Pirinkova gets Williams moving along the baseline, and forces the 23-time Grand Slam champion to scuttle one into the guts of the net.

Williams responds with a fiery forehand but is unable to reach a passing Pirinkova forehand that clips the line, nice. 30-30.

Punchy start to this quarter-final.

Tsvetana Pironkova is rattling down some meaty serves and fires her way to 40-0.

Another jumping serve out wide forces Williams long. A hold to love for the Bulgarian.

Pironkova edges in front on the Williams serve but the third seed quickly rattles to 40-15.

Williams has to stretch into a stray backhand and goes wide, but follows that miss with a booming ace down the T to hold.

Fascinating rally! Pironkova comes out on top with Williams at the net, clipping the tape with a forehand down the line that drops agonisingly on the American's side.

A solid opening hold for the Bulgarian.

Tsvetana Pironkova, with a heavily strapped left thigh, opens her quarter-final service game with a fizzing ace. The Bulgarian dips low into a slice and then skids a forehand winner beyond Serena Williams for 30-0.

Barry Cowan
Former British tennis player on BBC Radio 5 Live Sports Extra

Serena Williams changes ends the other side - I think that's intimidating. It's like 'don't distract me.'

Well-placed ace from Serena Williams as she dusts off an opening hold.

Williams barely lets Pironkova put strings on a ball as she races to 40-0. The Bulgarian is able to engage the 23-time Grand Slam champion off the next with a disguised drop shot, drawing Williams to the net, and executes delicate lob to win the point.

Barry Cowan
Former British tennis player on BBC Radio 5 Live Sports Extra

Serena has won quarter-finals for fun, she needs to put down a marker in this match, this is not just about winning, this is about saying 'Look, this is my court'.

And away we go. Serena Williams will serve first.

The winner of this one will face whoever comes through tonight's contest between Victoria Azarenka and 16th seed Elise Mertens.

Image source, Getty Images

For Serena Williams, the pursuit of a 24th Grand Slam singles title goes on as she attempts to equal Margaret Court's record.

The 38-year-old has won six times at Flushing Meadows and a seventh US Open crown would bring her level with Court, who won the last of her Grand Slam titles 47 years ago.

Williams, the third seed, has been taken to three sets in the past two rounds but has won all four of her previous contests with Pironkova.

Here we go! Serena Williams is out on court, rocking a red cape-coat, and ready to have a knock with Tsvetana Pironkova ahead of their quarter-final meeting.

Williams has been here a million times before, but I wonder if those nerves are nipping at Pironkova right now?