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Here's one for you: Roberta Vinci is the first woman with a single-handed backhand to make the semi-finals at the US Open since Justine Henin eight years ago. Henin was a player who used to give Serena a real test, but Vinci isn't quite in the same class, and from 40-15, she can't close the deal, allowing Serena to get back to deuce. But two tight shots from the American allow Vinci to hold her serve for the first time in four service games.

Well well. A slightly off-script beginning to the second set for Serena. She misses a simple volley, and then double faults to give Vinci 0-30. The Italian lies in wait for a second serve, and pounces with a return winner to bring up an unlikely three break points.

Vinci surrenders the first two, but she looks to have taken the third with a winner up the line - before Serena fizzes a quite brilliant, and demoralising, passing shot right onto the line. That's the last sniff that Vinci gets - Serena holds.

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Serena's mum Oracene is sitting in the stands as usual - there's a woman who has seen a fair bit of tennis in her time. She'll be familiar with the crushing return winner that Serena sends past Vinci, as she will with the primal roar of approval that follows. 

Vinci's serve is beginning to look increasingly vulnerable out there, a blowdart at a gunfight, and she sees another winner dispatched back past her to bring up two set points. The Italian fends them off, but Serena wrests a third opportunity, and she takes it when Vinci floats a backhand long. Business as usual on Arthur Ashe Court.

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A gorgeous drop shot from Vinci leaves Serena completely flat-footed, and the American sportingly applauds. It's a rare moment of respite for Vinci though, just her third winner, and Serena is increasingly dictating the terms of this match, stepping into court to crush a swing volley past the Italian. The number one seed is warming up nicely, like a microwave curry, and she steers a lovely half-volley off her toes to stretch her lead in what is beginning to look like a routine first set.

Ominous signs for Vinci. A disdainful swipe of a forehand return takes Serena to 0-15, and then a missed backhand from the Italian has her in a spot of bother at 15-30. Serena is fractionally wide with an attempted pass, but then Vinci misses with a loopy backhand and must fend off a break point. She can't, and Serena is in charge.

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Russia's Alla Kudryavtseva, who reached the quarter-finals of the women's doubles, has timed her tourist trip badly...

Never mind the kitchen sink, Serena is throwing the whole range of domestic appliances at her forehand. Two crushing winners bring up 40-0, and a big serve puts Serena back in front.

This is a big game for Roberta Vinci - can she put a bit of clear water between herself and the apex predator of the women's game? A tight forehand into the net shows Vinci's nerves, and then Serena pummels a two-hander to bring up break point. 

Another one duly follows, accompanied by a yell of 'Come on!', and Serena is back on serve.

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Well, well, well. Vinci has an opportunity to get to 15-30 on the Serena serve, but dumps a straightforward looking forehand pass into the net. But the Italian is not going quietly - she forces Williams to go long with a couple of punchy returns, and suddenly it's deuce.

Serena is looking a little cautious out there, and a couple of game points evaporate as Vinci strikes two winners: one mishit, one pummeled. Serena goes long, and whaddaya know, it's break point.  The Italian's spinny, swervy, slicy game is causing Serena some early strife, and the number one seed goes long to hand Vinci an early break. Might we just have a match on our hands?

Serena is immediately looking to come into the net and stamp her authority on this match, but she puts her approach shot into the net. Vinci uses a lot of slice on her backhand, which can trouble opponents for rhythm, but a couple of ominous groundstrokes from Serena take her to 30-30. Vinci scraps her way out of trouble though, and that is a very important hold for the Italian.

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An emphatic start for Serena, who immediately wangs down an unstoppable ace. A couple of unforced errors on both sides betray a bit of tension, before Serena again finds an ace. Another unreturnable serve, and that is a bruising, business-as-usual start for Serena Williams.

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Here we go...Serena to serve first...

Patrick Mouratoglou, coach of Serena Williams, tells ESPN: "I want everything to be free in her mind. She's playing a tricky player, with a great game but unusual for women, with a  sliced backhand and coming to the net a lot. Serena has to be completely focused and mask her emotion. I want her to use the stress to lift her level."

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The players are knocking up - both ladies in pink, Serena sporting a red, white and blue ribbon on her dress in honour of the anniversary of 9/11.

Piers Newbery
BBC Sport at Flushing Meadows

"'I played against her three weeks ago and the serve was.... incredible,' says Vinci. 'Not much,' is Serena's response when asked how much the rain delay affected her preparations. The pre-match interviews are understandably not usually too revelatory, and the American has looked especially glassy-eyed throughout all six she has conducted so far. A big cheer from the crowd, the headphones are removed, phone switched off and she is ready."

What do we know of Italy's Roberta Vinci? She's playing in her first Grand Slam semi-final today - she's a canny, guileful operator rather than a power player.

According to her profile on the WTA website, she's a good football player and her lucky charm is a stuffed orange dinosaur. 

So basically, this match boils down to this: the weight of history vs a stuffed orange dinosaur.

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This is the second oldest Grand Slam semi-final in the Open era, pitting 33-year-old Serena against 32-year-old Roberta Vinci.

I'm sure you don't need me to tell you that the oldest semi-final was the 1994 Wimbledon clash between Martina Navratilova (37) and Gigi Fernandez (30).