Must've been a Mouseslip

Online play this morning was odd. First I could get no advantage against a 900 rated player and that game was aborted because the Arena time ran out. Then, I was paired against a 1900+ (top .05% on a site that is 90% beginners) whose play left me confused.

Beginning at move five, my opponent's play was mysterious. We had reached a fairly normal position that can arise when White opts for the Catalan.

Black to move

I have had this position at least 283 times previously in online play, usually, but not always with White. In these games, both White and Black have performed within three points of their average rating with 138 White wins, 116 Black wins, and 29 draws. I have played 5...cxd4 and 5...Nc6, the two most popular moves.

5...g6?!

Only on Lichess, where the games database is huge, do I find any prior games with this move.

6.cxd5 exd5 7.O-O Bg7 8.dxc5

Black to move

8...Bf8? 9.b4

9. Nc3 was better. The one Lichess game with 8...Bf8 continued 9.Be3. It was a bullet game.

9...a5 10.Bd2?

10.Qa4+ Bd7 11.b5 Bxc5 and White is much better.

10...axb4 11.Bxb4 Nc6 12.Bc3

Black to move

12...Be7

White's poor play has restored Black to equality, but now White again has an advantage.

12...Bxc5 was the obvious move.

13.Nd4?!

13.Qc1 sets up a tactic to defend the pawn. To wit, 13...Bxc5 14.Bxf6 Qxf6 15.Nc3 Be6 16.Nxd5+

13...Bxc5 14.Nxc6

And after 14...bxc6, the game is interesting and roughly equal.

14...Qd6??

White to move

15.Nd4 Bxd4 16.Bxd4 Ra4 17.Qxa4+ and Black resigned.

I had thought that 14...Qd6 was a mouse slip, or maybe a premove, but the 5.5 seconds Black used rules out premove. It was a strange move in a strange game. 16...Ra4, then, looks like Black trying to lose.

My next game was against a player in the high 1600s and featured some strange maneuvers also, but not such that dramatically altered the evaluation. Here, though, I thought I had trapped White's queen.

Black to move

24...Rf6

24...Rxf5, which I considered briefly is the engine's choice.

25.Nxd6?

White should have played 25.Qxd6 Rxd6 26.Bxf4 and White will have a rook, bishop, and pawn for the queen.

I went on to win this game, too, although my opponent proved resourceful without a queen.

Far more satisfying than this morning's games was one that I played yesterday. At move 11, I had the opportunity to win a pawn, but spend a few seconds making sure that I was not missing a zwischenzug. 

Black to move

11...Ncxd4 12.Nbxd4

12.Nfxd4 Nxd4 13.Bd3 might be better.

12...Nxd4 13.Nxd4 Qxd4 14.Bxb4 Qxb4 and I nursed the extra pawn into the endgame, eventually winning.