For many years Augustin Santamaria was the key figure in Argentine bridge. Six times he won the South-American championship.
In this deal he spotted his only chance.

E/All		♠	K Q 5 2
		♥	A K J 10 4
		♦	4 2
		♣	A 4
		♠	9 8 7 4 3
		♥	5 2
		♦	K Q
		♣	10 7 5 2

¹Precision club: 11-15 HCP, five or more clubs; if only five, East holds a four card major suit as well; if six or more clubs a four card major suit is possible, not compulsory

West led the ♣J to dummy's ace.
Declarer played a diamond. East won with the ace, cashed the ♣Q (West the ♣6) and continued with a diamond.
Declarer won and played a trump, West following suit with the ♠6.

Santamaria knew West had no more clubs. Furthermore East had to have the ♠A (for his opening bid) and a major four card suit (since he had shown up with five clubs only). Since West had followed suit in spades, East's four card suit was in hearts - fortunately, because four spades in East would have doomed the contract.
Santamaria realised that - remember: East had the ♠A - if trumps were 2-2, EW would always be able to manage a trump promotion. This is how: suppose South now played ♠Q in dummy. East would win and play back a club. West would ruff with the ♠J or ♠10 and whether declarer would overruff with dummy's ♠Q or not, EW would be bound to score the ♠J or ♠10 (the only 2-2 trump distribution that would have allowed declarer to make his contract would have been the bare ♠J10 in West; since West had followed suit with ♠6 this distribution was impossible).
So Santamaria hoped the spades were not 2-2 and settled for his only chance: the bare ♠A in East!

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

So on West's ♠6 he played a small spade in dummy. He was rewarded with ten tricks when East indeed turned up with the bare ♠A and West with the ♥Q (in the doubleton, as we have already seen).
The latter was also necessary. This is why: suppose East possessed ♥Q (in his four card suit). After winning the ♠A, he would have played clubs, forcing dummy to ruff. After two more rounds of trumps (necessary to prevent West from overruffing the third heart) declarer could then have taken a ruffing finesse against that card in East, but the good hearts would have been inaccessible, since dummy had no more entry card.

For connoisseurs: there is a lot more to say about this deal: West could have given declarer a 'losing option' by not playing the ♠6 but the ♠J (better than the ♠10, read on). Declarer then would have had to guess:
- Covering with the ♠Q would be winning if West had ♠J10 alone.
- Covering with the ♠Q would be losing if West had ♠J106 (and East the bare ♠A therefore): East would play back a club and West would force dummy's ♠K by ruffing with the ♠6. After that the ♠10 would take the setting trick.
Should declarer cover the ♠J or not?
- The case for not covering: a 2-2 distribution is less likely than usual now that East has turned up with nine cards in hearts and clubs (so West has only four). The declarer therefore should forget the very slim chance of precisely ♠J10 in West.
- The case for covering: how many West players can read the situation that good to play such a seemingly illogical 'second hand high' from ♠J106?

Let's examine the deal still deeper: if East had held the bare ♠A10, after cashing the ♣Q he would probably (!) not have played a diamond but a club, hoping for trump promotion. This is another argument for the ♠A being bare in East.
This takes us to the reason why West's false card should be the ♠J rather than the ♠10. After all West hopes to convince South that East does not hold the bare ♠A. But holding ♠AJ alone East would, after having cashed the ♣Q, most certainly have played back a club (instead of the diamond) since West could then force dummy's ♠K with a trump as low as the ♠6.
In other words: since east has not directly played back a club, he certainly does not hold the bare ♠AJ whereas the bare ♠A10 is possible (though unlikely...).

And that leads us to our final conclusion: East has defended poorly. After having won the ♦A and the ♣Q, he should have played back a club instead of that crazy diamond. In the given lay-out that would have meant one down directly: West would have ruffed with the ♠6.
This defence would have defeated the contract if West had held as little as ♠J76, provided East, after winning the ♠A, would play another club. No matter what, West would then have made a trump trick for one down. Even if declarer had dropped the bare ♠A!