Tactics: Passed Pawns Must Be Not Hurried?

This week's Canadian Tactic comes from the game between US GM Maxim Dlugy and Canadian IM David Cummings at the 2015 Quebec Open in Montreal. Both sides have passed pawns, but White's King is an unstable blockader. White to play according to the cliché of your choice: "Passed pawns must be pushed" or "Do not hurry".

Hint: 

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White's main choice is between Qa5 and d5-d6. One move keeps White's pressure, and the other allows Black -- if he plays perfectly -- to draw.

 

Hint:

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In the game, White played 46...d6. The challenge is to calculate the long string of only moves for Black which draw.

 

Solution:

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See the game fragment below at move 46.
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 Round:  Result:

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This game, along with full annotations by IM David Cummings, will appear in the next issue of Chess Canada, the CFC's online newsletter.