A double fault from Pennetta - her first of the match - gifts Williams a 0-30 advantage. Tired-looking shots from Pennetta as Williams collects two break points. The Italian waving the white flag and who can blame her as a fierce Williams backhand flies by to seal another break. Williams roars. She knows she is nearly home.

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Williams dominant and the scriptwriters can start writing the final chapter. A hold to 15 - Pennetta wide on the final return.

Williams goes 0-30 up by punishing a timid second serve and is this where the top seed turns the screw? Oh la la! Williams with one of the shots of the tournament - running backwards, she retrieves and responds with a hooked a forehand-down-the-line winner. The top seed raises her arm to acknowledge the brilliance. Williams breaks to love. Pennetta in quicksand.

Two easy points for Williams for a 30-0 lead and the world number one fires down a 117mph ace to ease within a point of levelling the set. We have a rally! Pennetta on the back foot, moving hither and tither until she slaps a tired-looking backhand into the tape.

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Pennetta knocks herself out as she attempts a backhand from the baseline. Williams asks the Italian if she is ok, the 12th seed nods and gets back on her feet. Off we go again. Pennetta, slightly rattled, concedes a break point but is soon firing on all cylinders and wraps up the game with her sixth ace of the match.

Magical from Pennetta, who slides along the baseline to conjures up a jaw-droppingly good backhand winner down the line. The Italian rejuvenated while Williams is going through one of her dips.

Pennetta gathers two break points but, ultimately, they count for nothing as Williams rattles off a thunderous forehand and a booming ace to force the game to deuce. It was nervy at times (a double fault at advantage suggests this isn't vintage Williams) but a fourth and fifth ace of the match pulls the top seed through.

Pennetta screws a backhand wide and gives out a frustrated groan. Williams in contention at 30-30 and the world number one controlling her opponent, forcing her from tramline to tramline until break point is hers. Oh. Nice. A first ace of the match from Pennetta drags the game to deuce - but the 12th seed slips up once again. Although Williams fails to make the most of the opportunity and Pennetta stops the rot, another ace a first hold in what feels like an age.

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Williams coughs up two double faults to present Pennetta with two break points. The top seed responds with a brilliant one-two - a serve out wide followed by a crackerjack of a forehand winner. The Williams serve on song and danger is averted. Pennetta's return bounces beyond the baseline and it's game and first set Williams. Just the six consecutive games for the American.

At the start of this match there were indications that it might be the day of the underdog but Pennetta, who was loose-limbed and playing with freedom when the match began, is now griped by anxiety. Two break points Williams. One is saved but the Italian's backhand drifts over the baseline and Williams marches on.

A first ace of the match from Williams sees her skip merrily to a 40-0 lead. Pennetta not being given a whiff of a sniff on the top seed's serve. Another unreturnable howitzer. Boom! A stern-looking Williams in front for the first time.

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Earlier in this set Pennetta's groundstrokes were kissing the lines, but the Italian's radar seems to have been switched off. She saves two break points, but a fired-up Williams approaches the net and wrong-foots Pennetta with a thunderclap of a volley for a third break point. Pennetta stutters at the net and shakes her head as she makes her way back to the baseline. Advantage gone. Serena on the rampage.

At 40-15 Williams is in control, but she messes up a simple volley - netting when the court was at her mercy - and Pennetta now has hope. The duo battle it out from the baseline and it's the Italian who surrenders, netting a forehand. A stentorian "come on" from Williams greets Pennetta's error. The top seed is ready to rock.

Williams's feet now beginning to move in unison. The American not exactly dancing the cha-cha-cha, but she has upped her intensity and is hitting hard from the back of the court, which earns her three break points. Pennetta saves two but nets on the third and Williams nicks the game.

Interesting. Very interesting. Pennetta swinging loose and finding the lines - a fabulous forehand for 15-30 and it's a clench of the fist from the Italian has she goes a double break point up. Williams, out of sorts and moving at mobility-scooter pace, goes long on the next point. There's a hush on Arthur Ashe. The silence of a shocked crowd.

Williams strikes early, collecting a break point on her way to a 40-30 lead, but Pennetta holds firm, forcing Williams this way and that until the American balloons a forehand into the tramlines. The Williams forehand faltering and Pennetta comes through the test to consolidate her lead.

The defending champion is wearing an eye-catching black and white leopard print outfit. The American has come dressed like a snow leopard, but there's no cat-like reflexes from the world number one on the court. Pennetta moving beautifully, a delightful backhand the pick of the bunch as she secures an early break.

The warm-up is over. Pennetta is on the baseline, waiting for Serena to emerge from her chair. We've waited long enough Serena...

A Flavia Pennetta victory over two-time defending champion Serena Williams would cause jaws to drop into laps, but the top seed hasn't been her usual dominant self this year. Indeed, this is her first Grand Slam quarter-final of 2014 so she has been beatable on the grand stage.

Serena Williams warming up like a windmill at the net during the coin toss. The umpire in danger of decapitation. Both players getting into the groove after a later than expected start to this quarter-final thanks to the mammoth match between Stan Wawrinka and Kei Nishikori.

Thank you Michael. Aimee here to take you through to twilight. The theatre of a floodlit evening in New York, eh, where the lights shine at full wattage and those taking centre stage revel in the limelight. Some would say it is the perfect setting for those who usually sparkle under the Big Apple's darkened skies. First is top seed and five-time champion Serena Williams against Flavia Pennetta. Stand by.

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