2

In this game, http://www.chessgames.com/perl/chessgame?gid=1365631

The engine says that 20. Na5 is a blunder. However, I fail to understand why it is. Also, I am surprised at White's choice of moves here with c4 instead of Qxd6. Essentially he is giving a Bishop for free.

 [title "Bronstein vs Winter"]
 [fen "r2r2k1/pp3p1p/1n1B2p1/3P4/2q5/1N3P2/PbPQ1RPP/3R2K1 w - - 1 20"]

 1. Na5 Qa6 2. Qb4 Rxd6 3. c4?

What is the problem with 22. Qxd6 Qxa5 line where White gets a Rook and a pawn for his Knight and Bishop, the position looks equal. The engine says it is -3 for Black and gives a long long line but I am unable to see how it gives Black an advantage.

4

In the starting position, White should immediately protect his Bishop with 1.Qb4. Then, after 1...Qxb4 2.Bxb4 Rxd5, the endgame is close to equal.

Instead, after 1.Na5 Qa6, White's bishop is still under attack and his knight is vulnerable. The game continued 2.Qb4 Rxd6, and now if White plays 3.Qxd6, Black has 3...Qxa5. Black has won two pieces for a Rook since White's queen got overloaded.

You're right though that 3.Qxd6 was a better move than 3.c4, but only by about 0.40 according to Fritz. Both moves are under -2. The point behind 3.c4 is that White's f2-rook is attacking Black's b2-bishop and threatening to take it. The bishop wasn't already threatened by White's queen since after Qxb2 Black has ...Qxa5.

  • Thanks for your reply and pointing out that the rook hits the Bishop! I missed this trivial thing. But I am still unclear. If White had played Qxd6 instead of c4, material wise Rook and a pawn equals a Knight and Bishop. So -2 should mean there is some attack going for Black or Black can grab some material soon. It is unclear to me how this will happen. – Leg Dec 28 '18 at 17:15
  • @Leg The -2 comes from a lot of subtle (but important) factors. First, the only file White's rooks can really play on is the e-file. Meanwhile, Black's knight can immediately jump into play via the c4-square, and Black's bishop may be able to stir up play along the weak a7-g1 diagonal. White's king safety is also a problem, due to the weakened dark squares (e3 and f2), and the semi-back rank mate situation. Trying to resolve it with a move like h3 just weakens the king's position even more. Finally, White's queenside pawns on a2 and c2 are very weak. – Inertial Ignorance Dec 28 '18 at 19:01
  • @Leg don't believe those numbers that compare imbalanced material. A rook and pawn is NOT worth the same as two pieces. Two pieces are going to be better in nearly every situation except for a few endgames. – NoseKnowsAll Dec 29 '18 at 10:47
  • Yes, in general two pieces are superior to a rook and a pawn (especially in the middlegame) by roughly 0.5-1.0 – Inertial Ignorance Dec 29 '18 at 17:50

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