Well, someobody forgot to tell Kerber that her role in the Serena Show is that of the wilting supplicant...she would make a terrible understudy, by the way.
To be fair, Serena's footwork has never been particularly good - you certainly couldn't compare it to Justine Henin for example, whose footwork was nearly flawless - and as such when she gets nervous, that is usually the first thing to fail her. Boy did it fail her here. Time and again, she was hitting off balance, and frequently hitting reverse forehands from the center of the court for no reason other than she couldn't get her body positioned properly to hit through the ball - the reverse forehand is designed to maintain racquet head speed through a point of contact that is late. But that's not supposed to happen from the middle of the court - it's a bad sign when it does.
In addition to that, when she gets nervous her solution is rarely to dial down the power. Normally she just loads up and hits it harder, and that's exactly the wrong thing to do when you're nervous and your footwork isn't there. But here, one must give credit where credit was due - in the second set, she not only got a hold of her emotions, but she also began to massage the ball about the court more than just hit it. As a result, as well as Kerber retrieved, Serena wound up using that against her, because all she did was chase - i.e. no more attacking, no more short angles, no more flat shots up the line, she just chased. And it worked - despite playing her worst match of the tournament, she was able to get back on even terms by doing the exact opposite of her natural instinct to hit harder.
That's why I was so puzzled by her return to profligacy in the third set. The nerves must have struck again, because she was back to trying to out hit Kerber, and the result was, if not to be expected, certainly fitting. Once again, Kerber was able to surprise her with her defensive shots on the run that landed in strange places with weird spins, and when the moment came for Serena to kill the point she decelerated the racquet head and made errors. The worst feeling in the world is to miss being careful, which is exactly what happened to Serena. Unfortunately, when she tried to belt it, she also made errors, and by the end of the match I had the feeling that she was just confused.
As far as her forays to the net are concerned - I don't know why anyone would be surprised at how poorly she volleyed. But in this particular match, Serena was nervous, and that manifests in poor footwork. For the swinging volley you have to have your feet under you. You can't reach and stretch on that shot and get the proper combination of power and topspin - it's the only shot in tennis where you're encouraged to hit down on the ball. To do that properly, you have to be on top of the ball. Because her feet were a split second behind her mind, she was too far behind the ball to execute and wound up hitting up and out. She then switched to conventional volleys but her naturally poor technique combined with her nerves made her make a lot of errors. She also doesn't defend the net well, in fact, her net play is poor in general. Her approach shots are frequently indecisive, and her court positioning at net was almost comical. Covering the cross court pass when the down the line was the most likely option Kerber would take and vice versa. To defend the net properly requires a sense of where to go before the passing shot comes. Serena was even more lost at net than she was from the baseline.
At the US Open, Roberta Vinci did a good job of varying the spin on her forehand, hitting some deep with topspin, other times short and either side spin or simply flat, forcing Serena to hit up on her passing shots. Unlike Serena, Vinci has excellent volleys, and combined with a backhand slice that was alternately short and deep, preventing Serena from taking up a good court position, I gave credit to the little Italian for eliciting a lot of errors. I'm sure Serena was nervous, but I felt that it began with how Vinci was playing her, and got worse as the match went along. Here, all Kerber did was retrieve, and surprise her with the pace and placement of her defensive shots...the rest of it was just a case of Serena choking, nearly from the very first point.
There were two more problem areas for Serena, to name a few: first her serve abandoned her, and she didn't get the usual 1 to 2 free points per game that allows her to load up and really belt it in the rallies. Like Roger Federer, her game has evolved to rely on the serve, in order to function normally - when it goes off the boil, the game that seems so invulnerable suddenly appears to be anything but. It's not (as) hard to knock the cover off the ball and bludgeon your opponent into (typical) submission when you're up 30-0 every service game. But when you're in a hole from the off, the calculus, and more importantly, the racquet head speed suffers the consequences.
The second area that really failed her was the return of serve - which is normally a big weapon for her, and contributes to the standard capitulation of her opponents. Normally she is able to put a lot of pressure on that serve with the ferocity of her returns, but I don’t think she ever picked up the strange dynamic of a lefty serve, which was probably exacerbated by her nerves.
So suddenly Serena doesn't appear to be invincible. As readily as her contemporaries are to concede that she is, it just isn't the case when nerves combine with an opponent who either wittingly or unwittingly presents Serena with a style of play that is likely to elicit the worst from her under duress. I've always wondered what her opponents think they're doing when they try to out hit her. Heather Watson nearly made the upset of the decade at Wimbledon by doing a lot of retrieving and hitting aggressively when Serena allowed her to by taking some pace off her shots to manage her nerves. But everyone else (read Sharapova) tries to do what she does better than she does. That's about as clever as welterweight going toe to toe with a heavyweight in the boxing ring, and normally the results are equally distinctive.
But like I said, somebody forgot to give Kerber the script that ESPN had been working on since last September, and she just refused to do what she was supposed to do...namely lose. I think the clay will help settle Serena's nerves because even though she'll still be nervous, she will get more time to load up and hit with power when the opportunity comes, and she has enough power that she can hit through the slow surface. I'm guessing #22 comes at Roland Garros.
But I wouldn't call that bet into the bookies just yet...