Fuente: Julio 2014 ACBL Bridge Bulletin 
I spotted this particular defensive play some time ago and have been waiting for the opportunity to use it.
Both sides are vulnerable.
East has a pretty nice hand, one that he’d hoped to bid with. But the auction doesn’t give him a chance. North’s 3 was a limit raise, so bidding with the East hand is not a good experiment. There is some good news, though. West leads the 10, a choice East certainly agrees with. South wins the ace and leads the 3.
About 99% of the defenders in this seat would play low. After all, West is marked with just one heart and playing the ace might drop West’s singleton queen or king, which would cost the defense a trick. If East plays low, South wins his king, West playing the 2. South goes back to dummy in spades to lead an-other heart. East gets his ace but the A and the K are the only tricks left for the defense.
Here is the complete deal. Do you see a way to set 4 after West’s lead of the 10?
Because South has 10 ironclad tricks, it’s hard to spot. But South doesn’t know he is cold for 4. Perhaps you can find a swindle.
South wins the opening lead in the dummy (although he might duck and win the continuation). Upon winning the A, declarer does the normal thing, which is to start drawing trumps. On the first lead of a heart from dummy, East goes up with the ace – a potentially dangerous play. South and West play low hearts and now East continues with diamonds.
It is clear from the lead and subsequent play that East has five diamonds and West has only two. When East plays a third diamond, do you blame South for ruffing with the K? Do you blame him for then leading the Q, hoping to find trumps dividing 2-2?
Down one. This position is rare. East knows that South has the K Q x x x. Here, East has 14 points, dummy has 11 and South went on to game. South rates to have all of the missing points for his 4 bid.
Note West’s lead of the 10. Many players do not like doubleton leads. The truth is that a doubleton lead, when other leads look poor, is a good choice. West knows that East has some points. Leading the doubleton diamond has more going for it than the alternatives. The J 8 5 4 is not appealing.
The singleton 2 is dramatically bad -West may kill a heart holding in his partner’s hand. And, there is just no reason to lead it. A club from six low ones is kind of safe. But with no tricks to contribute, hoping for partner to have enough to set the contract is optimistic. Leading a diamond worked for a reason that no one could foresee. Color East’s play lucky, nuts or good – your choice – but it is clear that it is the only one to give South a losing option.