Over-extension. How could I have better taken advantage of it?

I recently have played a game where my opponent over-extended their centre pawns. I was caught completely off guard and didn't have any idea what I was doing. I then suddenly flipped the switch on the entire game by my opponent's blunderful moves. I feel like the won the game because of my opponent's mistakes, and not my own stratedgy or calculations. I am going to show you a game and I will need some help on finding a way to keep this same thing from happening to me again.

Post everything I did wrong below. I want to see it.

Hi, 
 in my opinion 3... Bd6 it's like commiting suicide, how do you counter his control over the e4-d5 squares?
after 4. Na5 a3 5. Na6 you don't have a nice position. moreover if you play N f3 white can play Bg5 trading the knight and you want almost no hope to get rid of e4 d5 pawns controlling the center..

maybe rather than 3... Bd6  which prevent you to push the d7 pawn and block the LSB you can try to play 3... exd4 4. Nxd4 Nxd4 5. Qxd4 d6. in this way you should be able to release the tension in the center and prevent the advacnce of the e 4 pawn.

7... Qe7 very nice tactical solution though 8. f4 would have kept the pression.

3...Bd6? is, because of the game, a poor move - 4.d5 Nb8 is maybe the "best". One "simple" line of theory is 3...exd4 4.Nxd4 Bc5 (not ...Nxd4, because 5.Qxd4 and the queen is not exposed to attacks, but dominates the board) with the idea 5.Nxc6? Qf6 and due to the threat on f2 Black is able to retake c6 without doubled pawns.

Notice, however, that moving the piece twice is irrelevant - what is relevant is whether your opponent won time to develop, and since d4-d5 is not a developping move he did not. (Though, of course, had Black played 4...Nb8 he would have spent two tempi to White's one).

7...Qe7! had to be seen before playing ...Nf6. But of course you saw it The previous poster's suggestion of 8.f4 is then met by 8...Bc5, and White starts worrying about his underdevelopment+weak f2 square problems.

12...Be5: why rush out of a1, since White cannot trap you? (There is always the b2-a3 route). Just take one more piece (12...Kxe7) instead.

I don't think the rest of the game can be improved for either side (White is lost already, and Black plays sensible moves).

His opening was the "Scotch". Look it up on http://www.chessgames.com and you'll see how the lines go. The more you play the less surprised you'll be by the different openings. :)

irontiger you shouldnt give a book move like Nxc6 a

"?" ...

Is it really a book move?

To be honest my "book" dates back from the 1980s but where is White's advantage in this line?

You are a beginner.  People are trying to be nice, but are probably giving you too much detailed advice to sink in.

Learn one thing from this game.  One.  Dont turn a bishop into a pawn.  3.  ... bd6 did exactly that, moving a bishop to a square where it had very little mobility and was stuck defending a pawn.  Terrible move.  If you learn this simple thing from this game, your one clear step ahead.  

If there is one thing to remember from this game, it is that knights should have a retreat square when a pawn threatens them. Having a bishop on d6 was not the major sin here.

The problem is that he never had a plan, micky. He just wanted to win material, and Qe7 was not a !, any person who wouldnt panic wouldve done that.

dont know the lines irontiger because I dont play them. But Nxc6 is a move that is already played by many GMs so it cant be that bad. Cheers

Bd6 is certainly a playable move. It is by far inferior to the main lines, but it is playable nevertheless.

Your first mistake and blunder was 4. Nd4??. This blunders the game. You just gave up the pawn for no reason and gave white the whole board.

4. Nce7 is the way to continue. Even Nb8 is playable.

Opponent blundered his advantage away with 7. e5? Something like Be2 or Bg5 is simple and winning. Position is about equal now.

Opponent blunders again with 8. Bg5. Whites position is now hopeless.

Generally, avoid moves like 3. Bd6 if you don´t know your theory. Altough playable, these moves require precise play to avoid sudden disaster as they are quite anti-positional.

Even if you know your theory, you probably won´t have much use of Bd6 here. It´s better to reserve your learning for solid lines where you can expect something.

I wanted to castle later on.

In addition, with the Queens of the board, its very unwise to castle unless they have 2 rooks (but you snapped one off for free)

I think 5. Nxc6 used to be considered pretty harmless but then Kasparov began to play it and predictably it became very fashionable. Kasparov's original idea was 5. Nxc6 Qf6 6. Qd2 dxc6 7. Nc3 but nowadays they seem to choose 6. Qf3. I've never really studied this variation and can't say I really understand what's the point of it. One thing I can suggest is that in the Kasparov treatment white has kingside pawn majority similar to exchange Ruy Lopez with the crucial difference that white still has both his bishops although in the white wins I've seen this rarely seems to be the decisive factor. 6. Qf3 is even harder to understand and I can't avoid the impression that if this is the best white can do this line won't remain very popular.

Harmless or not, there's absolutely no reason to label 5. Nxc6 as a mistake though.

This + take the bishop on move 12. White hasn't got a single piece attacking so there's practically no danger you will get mated even if you can't castle. Re8+Kf8 only takes one move longer than castling anyway.

I'm going to go with my countryman on this one. The only time when you shouldn't sacrifice your castling privilege for a whole piece is when you're in immediate danger. This clearly wasn't the case here.

This is far too categorical for my liking. Sometimes castling is warranted even with the queens of. Other times it's better to centralise the king directly but you must analyse every case separately taking account all the relevant factors in the position.