Hi Maria - My conclusions from this year's encounters with Vika are as follows.
(1) With your "normal style" - trying to get the initiative at any rate - there is currently little chance to beat Vika. Usually, there is enough pressure in Vika's shots to make you hectic and ensure that 70% of your "shots" result in immediate errors.
(2) In my view your best chance to beat Vika (and Serena as well) is to beat them by your superior physical constitution (assuming you still have such at your disposal). In other words: If Vika or Serena dominates for "one and a half sets", it's fine if it took them two hours to get there and made them work physically and mentally hard. I am 100% sure that at this point Vika's, but also Serena's, play will deteriorate and if yours only slightly improved, the win in 3 set could be yours. Think e.g. about the Wimbledon final this year when you won your first game at 1:3 in the second set aganst Serena. In the following game, you had 3 opportunities to break Serena but did not make any of them. That could have been the turning point ...
Following this logic, all exchanges in the first set and beyond should be kept as long as possible. You can do this - meaning a defensive, sometimes "Kerber-like" play without any unenforced errors - because it has been your successful tactics versus Li Na, who you are constantly beating since playing "safe" and let her make the errors. Of course, Vika is a different caliber than Li Na. But you may want to watch two Azarenka matches of last week in Linz, where Julia Goerges came back from 0:5 0:40 to 4:5 30:30 in the second set, and also Martic's second set against Vika rather should have been 4:4 instead of 2:6.
I have to be more precise. What I mean by playing defensive and safe is the rallies. In Beijing, Vika won 90% of those. If you were able to reduce this only to 70% (thus win 30% thereof), it may be enough to make the difference in the score. It typically comes to a rally, (a) when you serve and Vika returns very well or (b) when Vika serves very well so that you must be happy to have returned at all. Your tactics in all other situations seem to be clear:
Return as aggressively as possible. Your reading of her serve usually greatly improves in the course of the match. This will define your number of your breaks. At 15:40 or so, it may, however, sometimes be advisable to return conservatively and make her play a rally. The surprise factor and your quick legs may bring you the break!
When you serve and the return is harmless, you have to make absolutely sure that your next shot brings you the initiative, but not necessarily the point yet! Minimize the risk of these second shots (not closely to the lines but intelligently placed!). As long as you keep the initiative, the exchange can be going on an on. Let her run and make her deliberately tired in such situations!
When serve and she returns very well, try to come into some form of defensive rally, don't give her the point by an overagressive second shot error.
A general observation of your recent encounters with Vika was that even though the scores were in clear favor of Vika, you often had points in nearly every game to win it but never got it. Stay cool in these situations. There is no way for a guaranteed point for you, thus make a clear plan for that point and execute it. But try to avoid double-faulting at that stage, either play the relatively safest second serve possible, or play a kind of 70/80% "safe" first serve. In this respect, in Beijing your double-fault at 3:5 40:40 in the first set was a pity, given that you came from being down 1:5.
I must admit I was really annoyed about the last point of said first set in Beijing. It was what I am calling "an execution point" - there is no excuse to miss said ball at the edge of the net. The set would have been longer, Vika would have begun earlier to get tired etc. I want to repeat my advice given before: Even if such short execution ball goes to your backhand side, often there is more than enough time to run around it, change grip and execute it with your forehand! Your backhand shots are too predictable regards where they will be going (sharply cross court). Such point can make the difference!
Vika is in general difficult, as there is no obvious place where to aim your shots at. The worst is to play a harmless ball to her forehand. In most cases, she plays longline to your backhand, not a winner but very safe and rather nasty. Your usual emergency shot is to also play longline (flat if possible but with a high error rate) but then Vika's next forehand will come ... So if possible try to play cross-court, safe, soft and long (Julia had some success doing so). Last time in Beijing you tried to play a lot into the middle. Not a bad plan in general but (a) Vika showed that she nevertheless can play a lot of said balls hard to your backhand and (b) it is a very difficult shot for you (resulting in many errors of length). Vika also has a good backhand, meaning that longer cross-court battles with her tend to be in her favor. So it may be a good idea to play a backhand longline early on (before being in the defensive), not a winner but making her run to the other side.
I think it is a rather simple plan to make the girl on the other side tired. Think of your match against Vika in Rome 2011. Although she won the first set 6:4, it was clear that she was totally exhausted and consequently gave up at 2:0 in your favor early in the second set. That was no injury, that was exhaustion!
All the best and no fears of Samantha who only can beat you when you are in very bad shape.
Regards, Leopold2