Slav Defense/Loss to 1800 player: how to improve?

This is a recent OTB tournament game I lost to a player of the same strength as me (1800). My feeling is that I played poor positional chess and continuously failed to capitalize on his suspect play. Any comments/critiques on strategy or tactics are greatly appreciated.

Thanks Everyone

I looked at only the first ten moves and confirmed with a database to see what you did wrong at the beginning. 

(1) 3. Nf3 is more popular than 3. Nc3. Nf3 is one of the first moves White wants to play in the standard Queen's Gambit Declined (2...e6) because that prevents Black from safely playing the gambit ...e5, so that heuristic still applies in the Slav.

(2) Yes, 4. a4 is all wrong: (a) White wants to play Nf3 and e3 (or e4) as soon as possible; (b) White wants to control the center; (c) White wants to be able to kick the bishop at b4 if Black plays it there; (d) White here anticipates that Black will play ...b5, but ...b5 is a weak move for Black and is nicely countered by a4, so White just loses a tempo here for no reason other than Black might play a weak move. This move negates all those goals in a single step.

Thank you for the opening analysis and advice. I've looked into it, and I think playing 3. Nf3 dxc4 4. e3 works pretty well. Alternatievly, white can play 3. Nf3 Nf6 4. e3 to sidestep all of this theory that arises with 4. Nc3 dxc4 5. a4 etc.

I think people here are putting to much stock in the opening.  It is not difficult to outplay an 1800 in any opening in OTB chess, but for clarity a4 has certinaly been played in GM games so I wouldn't worry about that.  Nf6 into Nf3 falls back into high level games that has been played by So 3 times this year and Nakamura. and if you go into last year, Aronian has at least 4 games

I do prefer 3.Nf3 against the Slav because 3.Nc3 does allow dxc4, and if you don't play a4 (which isn't great) the knight is kicked and the position is very messy. This is similar to QGA mainline of 3. Nf3 and 4. e3, as there is no need to prevent b5 as black cannot hold the extra pawn without big concessions.

In your game black didn't try to play b5, and opening play continued along main lines until 8..h6?! which is a nothing move. It is not a big deal but does give you very slightly better as opposed to about equal.

Things were fine until the mentioned 14. e4?, which I would be skeptical about as black's position looks fine and tactics look rather unlikely.

You were a pawn down, but you traded sensibly and eventually got to a drawn endgame, which you again had problems when you didn't 39. h4 to prevent black's 39.. g5. While it is probably still drawn, it is more difficult when you have to look at both sides. If you played h4, the g3 pawn is too far for the king to get to, and if the knight moves away the black king cannot defend the pawn and stop the a-pawn at the same time.

Yes Mike, I agree that others are too concerned with the opening (perhaps including myself). I think I prefer the system with Nf3 rather than Nc3, but the middlegame is what matters where I can try to outplay my opponents.

Thanks for the analysis. This makes sense; it's good that you pointed out the move 39. h4. I think that would make the drawing technique much simpler.

I've slowly been learning that recently. Middlegame is the most important.