zydeco: Najdorf puts Donner through the wringer in this game. In his annotations, he's very impressed with Donner's defense.
Donner follows the game Portisch-Najdorf from Round 1, but with the difference that the knight is on e2 instead of f3. The problem is that, from e2, it's hard for the knight to protect white's weak link at c4.
Donner calls 11.b4 a "horrible move" and adds: "I cannot understand myself that I played the move again against Fischer in the 13th round." The point, again, is that c4 becomes very exposed.
16.a4, 20.Rb4, 23.Nxc5, and 27.Nf3 are all precise moves to hold the balance.
In their notes the players disagree about 18....c5. Donner thinks that it's too aggressive, and 18....Nd7 gives black a more lasting advantage. Najdorf thinks 18....c5 was the best try in the position, and Donner really had to be at the top of his game to survive.