Opening lead: king of hearts.
Most books on the play of the hand contain one or more chapters on the mathematics of bridge. Among other things, they list how suits can be expected to divide and the proper way to handle a large variety of card combinations.
One subject sure to be covered is the question of whether or not to finesse when you have 10 cards of a suit missing the K-x-x, which was declarer's problem in the spade suit in today's hand.
Mathematically, the percentage play is to finesse rather than try to drop the singleton king behind the ace. What this means is that if you experimented hundreds of times with this combination, the finesse would succeed far more often than the play for the drop.
South was fully familiar with the proper percentage play, but when the moment of truth arrived, he played dummy's ace and felled East's king! However, he had ample reason for rejecting the finesse.
West began by cashing the K-A of hearts and shifted to the deuce of diamonds, hoping his partner had the queen and that declarer would misguess which card to play from dummy. But South played dummy's king, which won the trick.
Then, without bothering to enter his hand for a finesse, declarer simply played the ace of trumps, caught East’s singleton king and so made the contract with an overtrick. Had he taken a trump finesse, he would have gone down one.
Declarer's decision to reject the percentage play was based on the fact that West couldn't have the king of spades after his first three plays revealed he had the A-K of hearts and ace of diamonds. It was inconceivable that he would have passed originally had he held the king of spades also.
Since East was thus marked with the king of spades, South's only hope was to find the monarch unguarded.
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