Serena Williams has been cyborg serene as she goes about her business today.

The American is apparently locked in on the first set at 30-15 up, but then throws up an inexplicable error, planting an easy put-away into the top of the net with Keys having already given up on the point.

30-30. Keys pushing hard in the rally, finding the back corners and asking questions. But Serena keeps fetching and then throws the switch, upping the aggression, finding the angle and stretching Keys beyond her limits.

They were the two key points and Williams bags the first set.

Jill Craybas
Former world number 39 on BBC Radio 5 live sports extra

"Madison had been serving well, but that was a really weak service game. It happened because of how aggressive Serena has been on the Keys second serve."

Image source, EPA

Now then. Serena Williams has a sniff at 15-30 and suddenly the hunt is on.

Madison Keys is under the pump and cracks as she duffs a second serve  just long. Her error confirmed by the Hawk-Eye review.

15-40  and two break points. Keys misses with her first serve, Serena is straining on the leash to get at her second and when it comes a crunching return seals the break.

Jill Craybas
Former world number 39 on BBC Radio 5 live sports extra

Image source, Reuters

"Both players are holding really easily. After the next couple of games, we'll start to see if they can keep holding to get to that tie-break."

They won't be able to sell this set of balls to the punters after the match is done.

They are going to be more bruised than a banana in the bottom of a school bag.

Serena Williams holds to love, swatting away a smash on the final point.

Madison Keys keeps the big-serving trend running. A hold to 15 that I was slightly distracted from by pictures of Eugenie Bouchard arriving at Flushing Meadows.

It was proper rehabbing rock star stuff, big shades, hoodie pulled up and a entourage of minders.

The Canadian, who pulled out of the doubles after a dressing room slip, is due to play Roberta Vinci in the singles later today.

This is a little bit like something from the days of Michael Stich andYevgeny Kafelnikov in the men's game.

Whopping great serves are snuffing out any sniff of a break. Rallies at a premium. Both players winning more than 80% of points behind their first serves.

Serena Williams is the latest to rattle through.

Image source, AFP

Jill Craybas
Former world number 39 on BBC Radio 5 live sports extra

"Madison is trying to take a huge swing because she knows the power of Serena. She's always aggressive, but she's being even more aggressive. It's the only way she'll be able to beat Serena."

Madison Keys' forehand wind up is like one of those great big Roman catapults.

You can see it cranking into life a mile off, but that doesn't mean you can dodge the impending destruction.

 She hammers away a mid-court bounce to take the game to 15.

Madison Keys is not going to be forced back into her shell. 

She has come out fighting fire with fire on return, using the power of the Serena Williams serve rather than being cowed by it.

Big swinging replies to the Serena serves. It is a tactic that is going to churn out a lot of errors, but it is undoubtedly her best bet. She nibbles off two points in that service game before Serena makes it over the line.

Jill Craybas
Former world number 39 on BBC Radio 5 live sports extra

"Serena knows how good a player that Madison Keys is. It's no surprise that she come out in this way because she knows the threat she poses."

Madison Keys guides her serve past a rather passive Serena with a bit to spare.

The world number one looked like she was using that game as a bit of sighter, cracking returns into the top of the net.

Lindsay Davensport is picked out in the crowd by the television cameras, having a bit of chuckle with a companion.

Does anyone do psyche-out stares like Serena?

The world number one collects three balls from the ball boy, discards one, steps up to the oche and takes a long, hard look down the other end of the court before finally launching into her service action.

It was a look that said  "you have been weighed, you have been measured, and you have been found wanting".

The action that follows backs up the pre-point mood music.

Serena holds for the loss of a point, crashing down with a big bolshy ace at 4-15.

Jill Craybas
Former world number 39 on BBC Radio 5 live sports extra

Serena Williams, still zipped into a white tracksuit top, gets down a sneaky couple of extra serves as the umpire calls time on the warm-up.

Serena to serve.

Image source, Getty

Serena Williams is on court a little earlier than she might have expected.

And that is thanks to sister Venus who walloped Anett Kontaveit of Estonia 6-1 6-2 in 50 minutes in the previous match on the main stage.

The winner of Serena v Madison Keys will be next for Venus, who offered some nice words after her win.

She was asked what it was like to be part of the most public sibling rivalry in sport.

 "Awesome," she replied simply.

"I'm so proud of Serena and I think she is proud of me."

The players are on court.

But not before lobbing up a few platitudes to an interviewer lurking in the bowels of the Arthur Ashe Stadium. 

Serena Williams sounds a little nervous as she unclamps the headphones from the side of her head to answer.

"She has a lot of power, I have to be relaxed and calm and keep having fun," she says.  

Image source, Getty Images

Image source, Getty

Madison Keys has a good woman in her corner for this match. 

Coach Lindsay Davenport had her own tangles with Serena at the tailend of her career and chalked up four wins from 14 meetings including one in the quarter-finals of the 2000 US Open.

Keys looked in pretty smart form in the last round, dismissing Agnieszka Radwanska 6-3 6-2.

Image source, Getty Images

Madison Keys is the next woman in the path of the Serena juggernaut.

The 20-year-old is the most promising of the new generation of American players and is unlikely to be a rabbit in the headlights.

She is one of the few players who can match Serena's groundstroke power and went toe-to-toe with the world number one in the first set of their Australian Open semi-final before folding 7-6 (7-5) 6-2.

Image source, Getty Images

Forget superlatives and poetry, just look at the brutal, raw numbers of Serena Williams' iron grip on the women's game. 

She has won her last 31 matches in Grand Slams, and her last 24 at the US Open. 

She has racked up 51 victories, five WTA titles and just two defeats in 2015. 

She has twice as many ranking points as world number two Simona Halep.

And, of course, she has won all three Grand Slams this year.

She is just four wins from that calendar-year clean-sweep full house.