Benko?

Recently a game was published in an article that included the following position:

This was called the Benko gambit. The position came about through a different move order than the usual Benko, but I have no problem calling this the Benko gambit.

In the typical Benko (1. d4 Nf6 2. c4 c5 3. d5 b5) black gambits the pawn on b5 before white plays Nc3 and therefore Nxb5 is not an option. In the position above, white could play Nxb5. The annotator's notes to white's 8. cxb5 were simply "No other move really tests Black's dynamic choice."

I'd like to hear what people think about the possibility of 8. Nxb5 in the above position.

What about Nxb5 Qa5+ Nc3 Ne4, looks pretty good for black.

I feel that it must have something to do with white's dark squared bishop being off the c1-h6 diagonal, and something like 8. Nxb5 Qa5+ 9. Nc3 Ne4 clearly takes advantage of this, but white can play 8. Nxb5 Qa5+ 9. Qd2 and it looks like he's not in any trouble. So I'm not sure that 8. ... Qa5+ is the refutation to 8. ... Nxb5.

After 8. Nxb5 Ne4 then 9. Qc2 defending b2 and attacking the e4 knight looks ok.

8. Nxb5 Ne4 9. Qc2 Qa5+ 10. Kd1 f5

Black looks good.

slack, why play 10. Kd1 instead of 10. Nd2. Of course black has an initiative in this position, but unless it comes to something white is going to play e3, Bd3 and 0-0 and have an extra pawn.

I suppose after 8.Nxb5 Ba6 9.a4 Bxb5 10.axb5 (cxb5 looks worse) a6 black has typical benko compensation, only he has traded off his white bishop (which often gets in the way of his queenside play in the accepted lines) for blacks valuable knight. White's queenside will be weaker than usual.

FYI, I think black's kingside rook is misplaced

I don't think there's anything "wrong" with Nxb5, maybe it's just not as good as cxb5? I don't know. Maybe the book move is the more active choice and would therefore test black more?

Forgot about Nd2, haha. :)

9. ..Qa5+ 10. Nd2 a6 11. Qxe4 axb5 12. Bxe7 Re8 13. Bxc5. Garbage.

with Nxb5, white allows black to develop quicker on that flank.  a pawn on b5 blocks the storm more easily.

ericmittens, at the end of your line, black is not threatening axb5 since the a-pawn is pinned. So it's white who gets some typical Benko action by playing d6 and creating long term play on the d-file, and quarantining the knight at b8 for a bit.

Ahh yes you're right...hmmm...

What about Qb6 followed by a6?

Ahhh Gonnosuke, so good of you to come support my favorite opening 

Gonnusuke, I missed the b2 weakness. Originally I thought after 11. Qxe4 axb5 white would be able to take on e7 as suggested by slack. But maybe going back to c2 12. Qc2 is fine for white since Bxe7 is still threatened. It doesn't seem like black can put anything together tactically since only the queen and bishop are developed. White is still hoping to play e3, Bd3, and 0-0 with a good game.

I think the conclusion that cxb5 is a well known Benko structure where white knows his long term strategic goal may have been the motivating factor behind taking with the pawn instead of the knight. Clearly there are complexities in the position after Nxb5 that white might have felt black was better prepared for, this is after all an unusual move order for black to choose to play the Benko.