The Main Line of the Perreux Variation of the Two Knights Defense was played in the Dimock event at least five times, providing a great resource for contemporary theory, since this line is rarely seen today. As the other games in the tournament showed, White does best to immediately pin Black's Knight at f6 with 14.Bg5! (rather than Torre's inferior 14.Re1?! after which his own Knight is pinned with 14....Bb4!). Black then does best to attack the opposing Knight with 14....Bb4! (much better than the tempo-wasting 14....h6?! as in Marshall-Bigelow), threatening to ruin the White queenside with 15....Bxc3 . White must prevent this at all costs, as the earlier game Torre-Marshall showed. But he must do so accurately....
Though White wishes to post his Knight actively on e4, this exchange is premature, since the Bishop at g5 serves the valuable function of protecting the d2 square and slowing Black's Rook's intrusion to the seventh rank. And there is no hurry to grab the Knight, since it is pinned and cannot run anywhere. Therefore, best was 15.Ne2! when the game Bernstein-Alvarez, Montevideo 1954 continued 15....Rd5 (to break the pin and double Rooks on the d-file) 16. Bxf6 gxf6 17. Rfd1 Rhd8 18. Rxd5 Rxd5 (White has gained much by exchanging off one pair of Rooks, which guarantees that Black will not be able to sustain his counterattack on the seventh rank) 19. Kf1 Rd2 20. Rc1 e5 21. g4! (White demonstrates the superiority of the Knight over the Bishop in this position by fixing Black's weakened Kingside pawns -- much as Marshall did in his game with Bigelow) 21....c5 22. Ng3! Rd6 (Black must surrender his attack and turn to defense) 23. Ne4 Rc6 24. c4 Ba5 25. Rd1 ± Bc7 26. Rd5 b6 27. Rd3 Bd8 28. Nd6+ Kb8 29. Nb5 Rc8 30. Rd7 a6 31. Nd6 Rc6 32. Rxd8+ Kc7 33. Nf7 1-0.
White's Knight is chased all around the board from this unstable central position - reinforcing the superiority of 15.Ne2!
White cannot play 18.Rc1? immediately because 18....Re2! threatens the deadly fork 19....Bd2! and prepares both to advance the central pawns with e5-e4 and double Rooks on the seventh with R8d8-R8d2.
Of course White dare not grab the poisoned h-pawn since 20.Nxh7? Rh8 21.Ng5 Bxh7+ 22.Kh1 Bf5+ wins. By retreating, though, the Knight helps to drive the Black Rook from the seventh rank.
Much better than the straightforward 21....Rxe1 22.Rxe1 e5 23.Nh4 or the interesting 23.Nd4!? and White might even gain the edge here due to Black's weaker pawns. White's response is forced since 22.Rcd1 Rxc2 is clearly winning for Black.
Much better than 23.c4?! which loosens White's pawns too much and surrenders the key d4 square, which can now be used as a post for White's Knight with the c3-pawn's support.
White must create some "luft" (German for "air") for his King lest he fall victim to a back rank attack - as, for instance, on 24.Nd4? (exploiting the pin on the e-pawn) 24....Rd8! 25.Nc2 (forced) 25....Rd1+ 26.Ne1 Bxb2! 27.Rxe5 Bxc3 28.Kf1 Rxe1+! (simplest) 29.Rxe1 Bxe1 30.Kxe1 Kd7 and the King and pawn ending with a pawn advantage (and a passed pawn at that) is a cakewalk for Black. But now Black gets to kick the Knight around some more....
An essential zwitchenzug (German for "in-between move"), since the Knight otherwise would help Black gain a winning advantage after either 28.Na7+? Kb8 winning it or 28.Nd6+ Kc7 29.Nc4 Rd5 and Black has complete control of the vital d-file. Now at least White forces off the annoying Black Bishop, after which his drawing chances are greatly improved.
No better is 28....Bxb2 29.Rxb2 (simplest) 29....axb5 30.Rxb5 with much better drawing prospects than in the game since 30....Rd5?! is met by 31.c4. And even worse is 28....Bg5? 29.Nd6+ Kc7 30.Nf7! and White's fork of Rook and Bishop wins material.
The importance of the d-file in this position is so great (in order to achieve any Rook activity), that White surely does best to surrender the h-pawn with 32.Rd2! Then if 32....Rxh2 33.Rd5! and White has excellent counterplay, since 33....Rh5? is met nicely by 34.g4! In fact, the d-file is so important, that if 32.Rd2 Black would do best to play 32....Rd6! when the King and pawn ending after 33.Ke2! Rxd2+ 34.Kxd2 is certainly difficult to judge, even though Black will have the edge. Now Black uses the d-file to completely dominate the remainder of the game.
If 34.Rd2 c4! creates complete domination for Black. The Rook would then be untouchable, since 35.Rxd6 exd6!+ creates a far-advanced, supported passed pawn for Black that keeps White's King tied to defending the d2 square. Meanwhile, Black's King marches over to the Kingside and picks off White's pawns there - and, once that is complete, uses zugzwang (German for "the compulsion to move") to force through the d-pawn. Play might go 35.Rxd6 exd6+ 36.Ke3 Kd6 37.f3 Ke5! 38.Kd2 (Black threatened 38....f4+! 39.gxf4+ Kf5! and White will be forced to give way due to zugzwang, allowing ...Kxf4 and ....Kxf3 winning) 38....b5! (Depriving White of tempi) 39.Ke1 h5! 40.Kf2 f4! (Black's breakthrough combination needs to be carefully timed and counted out, since it allows White to create passed pawns - and even a Queen! - as well) 41.g4 hxg4 42.fxg4 Ke4! 43.h5 f3 44.h6 d2 45.h7 d8=Q 46.h8=Q Qe2+ and Black either mates White or wins his Queen after 47.Kg3 Qg2+ 48.Kh4 Qh1+ etc.
Marshall gives up the d-file temporarily, only now that White cannot make use of it for counterplay (since 35.Rd5 Rxb2+ etc.). His plan will now be to blockade White's pawns on the kingside while advancing his own on the queenside for an eventual breakthrough, after careful preparation. Marshall's endgame technique is truly marvelous.
White desperately tries to bring his King to the defense of the weak queenside pawns. But there are weaknesses on the kingside as well.
Black has achieved his strong pawn placement in preparation for his King's invasion.
Black now has forced his way to complete domination.
A desperate attempt to enter a King and pawn ending. Likely White did not recognize that Black is still winning after the exchange.
Much more accurate than the immediate 47....c3?, which allows White to complicate matters after 48.bxc3 Kxc3 49.Kd1 Kd3 50.Ke1 e3 51.f3! e2 52.g4! creating his own passed pawn in a situation where Black cannot force through the e-pawn to a Queen. After 47....e3! this plan fails to 48.f3 e2! 49.Kd2 Kxb2 and Black will force through the c-pawn to the queening square.
There is no hope in 49.g4? cxb2+ 50.Kb1 fxg4 with mate in three moves.
It is rather remarkable to contemplate how White is lost despite being up a pawn in this simplified position! But Black has the all-important "opposition" (that is, his King forces his opponent's to give way), which is the key to winning King and Pawn endings. White's King is helpless on the back rank as his pawns fall. Note again that there is no hope in pawn sacrifices: after 50.e4 fxe4 51.g4 hxg4 Black will queen first with check!