S/EW		♠	A 3
		♥	K 5
		♦	Q 9 4 3 2
		♣	K 10 3 2
		♠	K 6
		♥	Q 7 6 4
		♦	K J 5
		♣	A Q J 6

West leads the ♠Q.
How should South play?

Solution

Declarer counts six top tricks and can set up at least two more tricks in diamonds. If that suit is 3-2, this is not a problem, since declarer can establish four extra diamond tricks while giving up the lead only once.
However, if the diamond split is unfavourable, the contract is in danger: if declarer loses the lead twice in that suit (or once in diamonds and once in hearts) the opponents will make at least three spades as well.
Declarer can guard against a number of unfavourable diamond distributions, i.e. these:
1. The bare ♦A with West. To overcome this 4-1 distribution, declarer must start by playing the ♦5 from hand: West's ♦A beats air and declarer has established four diamond tricks: an overtrick.
2. The bare ♦A, four diamonds to the ♦A or five diamonds to the ♦A with East. To overcome these distributions, declarer must play a small diamond from dummy twice (unless East goes up with the ♦A at once).
- If East goes up with the ♦A, whether perforce or voluntarily, declarer has four diamond tricks and an overtrick.
- If East (correctly in this case) plays a small diamond both times, declarer has made two diamond tricks without having lost the lead. Next he sets up a heart trick, his ninth.

Case 1 concerns one specific 4-1 split.
Case 2 concerns five specific 4-1 splits (West can have four different small singletons in diamonds) and one specific 5-0 split.
Declarer takes his best chance, so he guards against the distributions in 2:

S/EW		♠	A 3
		♥	K 5
		♦	Q 9 4 3 2
		♣	K 10 3 2
♠	Q J 10 9 8			♠	7 5 4 2
♥	A 10 8 3			♥	J 9 2
♦	6			♦	A 10 8 7
♣	9 7 5			♣	8 4
		♠	K 6
		♥	Q 7 6 4
		♦	K J 5
		♣	A Q J 6

He takes the lead with dummy's ♠A and plays the ♦2 to the ♦J. If West wins (unlike here), declarer will have to hope for the suit to be divided 3-2.
Here the ♦J wins the trick, however. Declarer now does not continue with a 'lazy' ♦K, since this will lead to down on the actual distribution (East wins with the ♦A and plays a spade back: South has only eight tricks for the taking and as soon as he loses the lead to a red ace, he will lose five).
Therefore he meticulously crosses to the ♣10 and plays the ♦3. Again: by going up with the ♦A East would allow declarer to make an overtrick.
So a good East will duck and South wins with the ♦K, still having his second spade guard. If West follows suit with a small diamond (unlike here), declarer simply clears the suit, making an overtrick.
But here West shows out. Having two diamond tricks in the bag, declarer now safely establishes a heart as his ninth trick.