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.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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