The exchange cxd5 at move 4 is a little bit of a commitment. After 4. Bg5 Be7, White can still play the exchange, but has other options open as well...even after 5. e3 or 5. Nf3.

As black, I prefer transposing to the Semi-Slav with c6.

I don't understand why your opponent would take 10 minutes to make this move. It is quite obvious. Thinking so long is a 'tell'. If a move is obvious, then just take it. Sure there might be other possible moves. But if your opponent is clueless in OTB, he shouldn't let you know. Besides, your next move might help him to develop an adequate response without expending so much time.

It would be interesting to discover what White thought about during these 10 minutes. Confronted with something new, confidently played, it was probably worth checking out whether Black 'knew' something. Mind you, it is hard to see 11.0-0 being bad in this position. He could have played it fairly quickly - not too quickly - as a prevaricatory move...

Actually people usually do that when someone gets out of their preparation. I think they check: 1. if the unexpected move is actually a mistake 2. what is the plan behind the move. I did think that 10 minutes is a bit much though   He was probably considering should he play 11.0-0 (which is good) or 11.0-0-0 (which is absolutely the wrong idea here as I explained).

I would have spent some time looking if after o-o, b5 leads to something, followed by Ka6 or even b4, Ka4, Qc7 or Bd7...

I hope you used his time to decide this. If you played instantly, then it would have freaked him out...especially since you have a higher rating than he does.

Yeah, I played it pretty quick - the reasoning I explained above is not complicated and does not require much tactical checking.

I don't see anything wrong with this plan, except for one circumstance. White wasted 10 minutes on a previous and obvious move against a higher rated player. Opening the game may be dangerous against a higher rated player; but as an expert, he should be able to hold his own tactically as long as he does not get himself into time trouble.

Well the rating difference is not as important as the objective quality of moves. The problem is that his whole plan with quick 13.e4 is not the best way to treat this position (12.f3 by itself is not a big mistake).

Usually when there is a knight on f8, the king-side is a hard 'nut' to crack (attack). White was going to have to deal with that fact, regardless of his plan.

I view this as a bit of a mistake on White's part because it allows Black to equalize. The purpose for f3 was not to immediately open up the game, but to control e4 and g4. The move e4 needed to be done at the proper time. White's timing is all wrong here. But given his immediate choice of the exchange variation, this should not be too much of a surprise. Perhaps he was thinking in terms that the resulting pawn structure would be winning for White in an endgame. Yet, there are too many pieces still on the board to be concerned about that. Effectively, this structure in this circumstance just gives Black more targets to attack.

Something to be borne in mind is that White's pawn centre is a hanging pawn couple sitting on files open to Black's rooks. Such a pawn couple can be very vulnerable...

If 15.e5 Nd5 16.Bxe7 Rxe7 one would ordinarily be very reluctant to exchange on d5. Unfortunately the threat of 16...Ne3 forces his hand, rather (17.Qe2 Ne6, maybe?).

The exchange with 17.Nd5 is meant to improve Ne2 after 19.Nc3, while taking out the centralized Black's Knight (in effect swapping bad Ne2 for good Nd5) - but of course 17.Qd2, Ne6 is also equal so we can say it is just a matter of preference.

IMHO, this is not too bad. I agree that 15. ...Ne6 would have been better. *** IMHO, 14. ...Bg4 was a far worse mistake for reasons you already stated in comments.

Here we disagree   I think that 14...Bg4 is not exactly a mistake, it is a solid move but not the best one (14...Ne6 is slightly more precise), while 15...Qd7 actually gives White the advantage if he plays the best move.

That White's central pawns control much of the centre is an important consideration, but the pawns themselves constitute a target for Black. I understood that right now a battle was raging around these pawns. White might be interested in advancing the e-pawn in order to achieve what Nimzovitch used to call a "blockaded security"...

lighttotheright - I think exchanging pieces is not the best plan for White with those pawns. Neither one is a passer, although after d5 push there will be one on the d file. But if otherwise material is the same, it can also be a weakness in an ending - namely if Queens are off the board then the Black King can approach and take it out. Usually a better plan is to use the pawns dynamically for middlegame action and then look for a favourable ending. iondowman - That is the idea, White can use the spearhead on e5 to pressure Black's kingside, while keeping the d4 pawn well defended.

I believe you are underestimating the number of White's choices here, but I agree that Nf4 seems a bit weak. White should be looking for favourable ways to exchange pieces for an endgame advantage. Pushing either pawn seems almost pointless to me at this particular moment. They are a very strong center duo controlling key center squares. If you push either one, you weaken both. The eventual e5 push is the better of the two, because of the potential king-side attack. Again, a more promising strategy for white is to exchange off pieces while keeping in mind the other strategies should opportunity present itself. Flexibility is key here. **** Dynamics, Yes. Perhaps I overstated things slightly. You don't want to exchange off everything. The potential advantage for white is really in a end of the middle-game. My endgame is so extensive that sometimes I forget that technically it is still the middle-game. The reference is Hans Kmoch "Pawn Power in Chess" page 12. There are distinct advantages and disadvantages with this formation. Moving one of the pawns does weaken both unless done with significant purpose. *** Have you considered the potential for white to play 16. h3? In that case, Bg4 is shown to be the bad move it was. White might have been able to exchange favourably had he done this.

Although this allows white to begin exchanging off pieces, the redeeming value of this move is that the exchange is equal.