Both players are a tombola of shots, you don't know if you are going to pull out a pearl or a dud.

A blockbuster of a forehand from Coco Vandeweghe following a Venus double fault gives Coco 30-30.

But the Williams' serve snaps back online with a clumping ace and then another thumping tee off is too hot for Vandeweghe to handle.

Coco Vandeweghe flirts with disaster, slipping to 0-30, before pulling herself back into shape and keeping the gap at just one break as they head into the final furlong.

The chance was sitting up and begging at 30-15 down for Coco Vandeweghe, but she sends her forehand fizzing wide with open acres of blue court to aim at.

Venus Williams' 10th ace of the mark skids across the centre line and away to seal the game.

Coco looks like she is sinking into her own skin at the moment.

Coco Vandeweghe could do with a pair of oven mitts with that.

She pulls the game -and possibly the match - out of the fire at 0-30 down.

A cracking forehand that wrong-foots Willliams is followed by twin rocket serves.

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It doesn't matter what they look like now, so long as the service games keep transferring from racquet to scoreboard for Venus Williams.

She holds to 15 as Coco bumps long.

That was more like it from Coco Vandeweghe. 

She holds to love, but she needs more than that now.

Venus Williams is four straight service holds from a first Grand Slam final in seven-and-a-half years.

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Coco Vandeweghe just does not seem to have the big-point stones.

Another two break points go slithering past without her being able to take advantage.

Venus, by contrast, hits a cleaving ace for deuce and then plays relentlessly sensible percentage tennis to win the next point and escape.

Coco is facing a rack of personal gremlins and demons now, not just one of the all-time greats.

David Law
Radio 5 live commentator

I covered my first Australian Open in 2003. Roger Federer had yet to win a Grand Slam title and went out in the fourth round. He was regarded as one of the game's underachievers who might not deliver on his talent. I'd never heard of Andy Murray. And I had brown hair, (not grey) as I interviewed champion Andre Agassi. 

In the women's final, Serena Williams defeated Venus Williams. 

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Venus Williams whips away a forehand winner to bring up break point and 30-40.

Coco drills down a piledriver serve to register an ace and knock her back.

Less impressive serving now though. A double fault gives Venus a second look at break point by return of post.

Into an exchange and it is the Vandeweghe backhand that goes flaky first.

Break Williams.

We need to talk about Venus Williams' visor/skirt combo by the way. An extraordinary tie-die day-glo coordinated combo.

The killer stat from that set was the break point conversion rate.

Coco was zero from seven. Venus was two from two.

To misquote Lady Bracknell, to lose one might be misfortune, to lose seven looks like a bad case of the jitters.

Venus Williams socks down her fifth ace of the set to move to 30-0 and to within two points of the set.

Coco Vandeweghe lamps one of those brute cross-court winners to keep her honest at 30-15.

A Williams frame-botherer flies wide for 30-30. And then Williams contrives to drive a ball straight at Coco from the net and Vandeweghe floats a chip shot back. Williams allows it drift by and...IN!

Break point. Coco loads up on return, but smears her shot wide, hanging her head between her knees.

Williams is finally across the line as that much-improved serve delivers an ace on the final point of the set.

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Coco Vandeweghe keeps her cards on the table, but Venus will serve for the second set and parity next.

Venus Williams sees off another break point as she soaks up the best angles that Coco Vandeweghe can throw at her and then eases a winner up the line.

Coco twangs an ambitious backhand into the net to finally give way and that is surely any hopes of salvaging the second set toasted,

The momentum is swashing around in this one like grog on a pirate deck,

Coco Vandeweghe races to 0-40 and three break points.

She wallops a backhand down the line on the second, but the ball flies just a little too long before the topspin can bite.

Deuce.

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Coco Vandeweghe has taken a look at the view, realised how high she has climbed and got a bad dose of vertigo.

Back-to-back double-faults turn a sticky situation at 15-30 into a gift-wrapped double-break for Venus Williams.

We look locked on for a decider.

Coco Vandeweghe - looking for the immediate reply - forces break point. Venus Williams knocks her back with a lovely dipping cross-court forehand.

Another chance from deuce. And Venus Williams plucks a ramrod ace out of the quiver to see that off as well. 

Another popper, this one zeroing in on Coco's sternum like a heat-seeker, sees her out of danger.

Suddenly the pizazz in Coco Vandeweghe's game goes up in smoke.

She duffs three successive backhands into the net and sends her racquet tumbling end over end in the air in frustration as she is broken to love.

Settle in, fill a thermos, this could be heading long. Way long.

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Venus Williams needed a foothold because she was in danger of being punched drunk by Coco Vandeweghe's blizzard of powerful groundstrokes.

That hold to love is a platform to build the start of a comeback on.

David Law
Radio 5 live commentator

Between Wimbledon last year and the Australian Open, Vandeweghe’s win-loss record had been 3-7. On paper that equates to a player with very little confidence, but she carries herself with immense self-assuredness, jarringly so, for some, at times. Her tennis this fortnight is matching up to it - wins over Eugenie Bouchard, Angelique Kerber and Garbine Muguruza were no fluke, and she is now in command against Venus Williams. 

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