If you duck the diamond and West has a singleton, you are toast. If you duck and West started with a doubleton diamond, you are still toast. East wins, plays a club over to West and a spade return does you in while the diamonds are blocked.
The bottom line is that you can’t make the contract if you duck the diamond so you have to win the ♦A and play West for both spade honors. The fact that West did not bother to cash a high club bodes well that he has both spade honors and a singleton diamond.
Say you overcome the first hurdle and play the ♦A. Now what? What you shouldn’t do is draw West’s last trump and lead a spade honor. Why? Say West, who you need to have both spade honors, covers and you duck. Now West cashes a club and gets out with his other spade honor which you win with dummy’s ace, carefully unblocking your remaining spade honor. You have nothing left but to cash the ♠9 and hope spades break 3–3. I have news for you: They don’t. West has the ♠K Q doubleton.
The error was to lead a trump when you were in dummy with the ♦A. What you have to do is lead a low spade to the jack and queen. Say West wins, cashes a club, and gets out with a high spade to dummy’s ace as you unblock the 10. With a trump still in dummy, you can lead a trump to your hand and run all your
hearts reducing to a spade and the ♦Q. Dummy remains with the ♠9 7. East, has to either discard a spade, ceding the last two spade tricks, or ditch the ♦K, equally fatal.
What if West does not cash a high club before getting out with a spade? You can counter that defense in one of several ways. Win the ♠A, unblocking the 10, of course, come to your hand with a trump and concede a club. West, club flush, leads a club, which you ruff. Again, you run off all of your trumps to squeeze West.
You might wonder what would happen if West exited a heart upon winning the ace, prematurely removing the entry to the closed hand that led to the eventual squeeze. You win and lead the ♠J, covered by West. (Remember the ♦A is still in dummy). If you duck, West exits with a diamond and down you go. If you win the ace and lead a spade to the 10 and queen, West cashes a club and exits a diamond and down you go as you can’t get back to your hand to play your trumps and squeeze East. Do you see what you have to do? After you lead the ♠J and it is covered, you must win, cash the ♦A (a sort of scissors coup) and get out with a spade to the 10 and king. West can do no better than win, cash the ♣Q, and lead a third club. You ruff, run the hearts and squeeze East. Of course this line doesn’t work if spades are 3–3. West ducks the second spade and down you go! A cute deal all around.
Thanks to Howie Weinstein, a Los Angeles transplant (sort of), who unsuccessfully played 4♥ against this pair, the eventual winners of the Cavendish Pairs.