After nine rounds of the 11-round US championship, grandmaster Wesley So leads with 8 points. GMs Jeffery Xiong and Ray Robson are tied with 7.
In round 9 on Wednesday, So and Robson — seconds apart — simplified to pure pawn endings (the easiest type of ending to win) by sacrificing rooks for bishops when they knew their kings would occupy a critical square afterward.
In any endgame of king plus pawn vs. king, the strong side should suss at a glance if it’s a win by either 1) queening the pawn because the enemy king is “outside the square of the pawn “, or 2) occupying one of the pawn’s “critical squares” with the king.
[FEN "8/5k2/8/3KP3/8/8/8/8 w - - 0 1"]
{[#] If the pawn is on the fifth or sixth rank, then the critical squares are three files wide, one rank ahead. With White to move, the critical squares for the e5-pawn are d6, e6, f6.} 1. Kd6 Ke8 2. Ke6 1-0 *
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[FEN "8/5k2/8/3KP3/8/8/8/8 b - - 0 1"]
{[#] Black to move can hold the white king off its critical squares.</br>} 1... Ke7 2. Ke4 Ke6 1/2-1/2 *
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[FEN "k7/8/8/8/4P3/8/1K6/8 w - - 0 1"]
{[#] If the pawn is on ranks 2-4, the critical squares are three files wide, two ranks ahead. A pawn on e4 has critical squares d6, e6, f6. White wins with the “overpass”, heading straight to f6.</br>}
1. Kc3 Kb7 2. Kd4 Kc6 3. Ke5 Kd7 4. Kf6 Ke8 5. Ke6 1-0 *
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[FEN "k7/8/8/8/4P3/8/8/3K4 w - - 0 1"]
{[#] This one is the “underpass”.</br>}
1. Kd2 Kb7 2. Ke3 Kc6 3. Kf4 ({</br> White must “underpass the e4-pawn to reach “the “outside critical square” f6:} 3. Kd4 $4 Kd6 $10{.</br>}) 3... Kd6 4. Kf5 Ke7 (
{</br> If} 4... Kd7 {, then White has to remember to occupy the critical square: } 5. Kf6 $1 $18 (5. Ke5 $4 {or 5. e5??} 5...Ke7 $10{).</br>}) ) 5. Ke5 1-0 *
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[FEN "8/8/2k5/8/7p/8/5KP1/8 w - - 0 1"]
{[#] White must know the underpass maneuver, else accidents happen. </br>}
1. Kg1 $1 (
{</br> If } 1. Kf3 $4 {, then} 1... h3 $1 {draws. } 2. gxh3 {is a sad rook pawn:} (2.g4 Kd5 3.Kg3 Ke5 4.Kxh3 Kf6 5.Kh4 Kg6 {=}) 2... Kd6 3. Kg4 Ke6 4.h4 Kf6 5. Kh5 Kg7 {.</br>} )
1... Kd5 ({<br> }
1...h3 2.g3 Kd5 3.Kh2 Ke5 4.Kxh3 Kf5 5.Kh4 Kg6 6.Kg4 +-
{</br>}) 2. Kh2 Ke4 ({</br> }2... h3 3. Kxh3 $1 $18 { (other moves draw; the student should work this out)</br>} ) 3. Kh3 Kf4 4. Kxh4 1-0 *
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[Event "2020 U.S. Championship"]
[Date "2020.10.28"][Site "https://lichess.org/cFqFCqbU"]
[White "W. So"]
[Black "J. Xiong"][FEN "3qr1k1/5ppp/p7/3p2P1/1Q5P/2PB1b2/1P1R1P2/2K5 w - - 0 26"]{[#]} 26. Bxa6 ( {</br> Black is a pawn down, making the simplification: } 26. Bxa6 Re1+ 27. Kc2 Be4+ 28. Bd3 Bxd3+ {unappealing, and his isolated d-pawn is on the wrong square color for bishop mobility. At a time control of 25 minutes per game plus a 5-second increment, Xiong spent almost 13 minutes here. </br>} ) 26...h6 ({</br> White’s king is exposed, but the attack} 26...Qa8 27. Bd3 Re1+ 28. Kc2 Qa1 {isn’t possible yet, for} 29. Qb8+ {, so …h7-h6 makes <em>luft</em> (possibly), and loosens the white kingside .</br>})
27. gxh6 Re4 28. Qc5 Rxh4 29. Qc8 ( {</br> It’s safe to interpolate} 29. hxg7 {.</br> } ) 29... Qxc8 30. Bxc8 30... Rxh6 ( {</br> Black can create a passed pawn of his own, but White’s initiative might’ve steered him away from taking on three weak pawns:} 30... gxh6 31. Bb7 Rh5 {.<br>} ) 31. Bb7 31... Rh5 32. b4 { </br> Passed pawns must be pushed.</br>} 32... Kf8 33. Kb2 { </br> Kings must be active in the endgame.</br>} 33... Rf5 { </br> Unpinning the d5-pawn.</br>} 34. Kb3 34... Ke7 35. Ka4 35... g5 {</br> That’s Black’s potential passer, and when it reaches g4, the bishop is guarded well enough for the rook to play more actively.</br>} 36. b5 36... Rf4+ 37. Ka5 37... Kd6 38. b6 ( { [#]</br> A difficult position for Black. King sealed off from the c-file, and the rook needs three moves to get behind the b-pawn. The positional problems are hard, and there’s even a tactical threat:} 38. b6 -- 39. Bxd5 $1 Bxd5 40. Rxd5+ Kxd5 41. b7 $18 {</br>.} ) 38... Rc4 $1 ( {</br> If} 38... Rc4 39. Bxd5 $4 {, then} 39... Rc5+ $19 {.</br>} ) 39. Rd3 Rc5+ { } 40. Kb4 { } 40... Rc4+ { } 41. Kb3 ({</br> Repeating moves suits the player who’s satisfied to draw, and the increment puts time on Black’s clock, so White doesn’t need} 41. Kb5 Rc5+ 42. Kb4 Rc4+ {to persuade him to move the king back to the third rank.</br>} ) 41... Rf4 42. c4 { </br> The d5-pawn is pinned in two directions, which is a neat trick with such little material on the board.</br>} 42... Kc5 43. cxd5 43... Rb4+ 44. Kc3 44... Rxb6 $2 ({</br> }44... Be2 45. Rd2 Rc4+ 46. Kb3 Rb4+ {is likely drawn.</br>} ) 45. d6 $1 45... Rxb7 {</br> Other moves are worse.</br> } 46. d7 46... Rxd7 47. Rxd7 47... f5 $2 ( { </br> Another slip in time pressure. Understandable, because if Black can trade off the f-pawn, it’s probably drawn. But if the pawn sticks to the second rank, the white king can’t capture both pawns as readily. } 47... Bd5 48. Kd3 Be6 { is more taxing.</br> } ) 48. Kd3 48... Be4+ 49. Ke3 {</br> White’s in position to win with Rd7-g7xg4.</br>} 49... g4 { </br> Though White can’t play 50. Rd7-g7 now because 50…Kc5 -d5 guards the bishop.</br> } 50. Kf4 50... Kc6 51. Rf7 51... Kd6 52. Rxf5 $1 {[#]</br> The easiest endings to win are pawn endings.</br>} 52... Bxf5 53. Kxf5 { plus 54. Kxg4 puts the king on a critical square for the f2-pawn, and if 53…g3, then the Kf5 is already on a critical square for 54. fxg3.} 1-0
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[Event "2020 U.S. Championship"]
[Site "https://lichess.org/jy7fbOYR"]
[Date "2020.10.28"]
[White "R. Robson"]
[Black "H. Nakamura"][FEN "8/R4Q2/3q4/6P1/6k1/3b4/6P1/7K w - - 1 53"]{[#]}53. Qd7+ { </br> Forces the queens off. </br>}
53... Qxd7 54. Rxd7 54... Bf5 55. Rg7 55... Bb1 56.
Kg1 {</br> The critical squares for the g2-pawn are f4, g4, h4. The white king steps out toward f4, before simplifying to king plus one pawn. </br> } 56... Bf5 57.
Kf2 57... Bb1 58. Ke3 58... Bc2 59. Rc7 59... Bf5
60. g6 60... Bxg6 61. Rg7 61... Kf5 62. Rxg6 $1 62...
Kxg6 63. Kf4 1-0 *
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