The Anti-Finesse Force
This is board 23 (rotated) from the September 7, 2017 afternoon session of the Irvine regional. 17 pairs (65%) ended up in 4♠, with only two Easts daring to double. The remaining pairs languished in a spade partial with the exception of two E-W pairs allowed to play 3♦, once undoubled! Half the declarers in 4♠ succeeded.
Against 4♠ the defense has two trump tricks perforce and plenty of time to establish a heart. But is a fourth trick available? The answer is yes and fundamentally it comes down to a position similar to this one:
If declarer or dummy has the lead, a trump finesse takes all the tricks. But if the defense is on lead, a heart force destroys the trump finesse even through an entry remains to dummy. However, this is hard to see for the full hand, even double dummy, because hearts must be played twice to setup the force and they cannot be started by West owing to the ♥J in dummy. Nonetheless, East’s trump holding is so strong that the defense has time to carry out this plan. (In practice, I led the ♥K and double dummy that killed the defense.)
Back to the full hand. Suppose West leads a diamond. Declarer cannot allow a club to be ruffed low or allow all of East’s honors to become winners. So he forced to work on trump and try to make the most of his ♠9. When a small trump is played from dummy, East must cover with an honor to prevent the deep ♠9 finesse. In practice I suspect East often played low and many declarers took the ace and played a second round hoping to reduce the defense to a single master trump before working on clubs. Down one. For this card combination, finessing the nine gives declarer an 89.6% chance of taking two trump tricks. Playing the ace requires a 3-2 split or a stiff honor in West’s hand, a 76% line.
Declarer might let East’s trump honor hold the trick in which case East must attack hearts. If declarer ducks the first heart, West wins and must continue a low heart to declarer’s now bare ace. Declarer is now doomed. He still needs to work on spades but doing so subjects him to the third round heart force which destroys the ♠A9 tenace over the ♠K8. Even the anti-percentage line of returning to dummy with the ♣A, playing for queen-doubleton, and leading a second low trump fails. East inserts another honor and regardless of what declarer does he is eventually subject to the heart force. The specific line of declarer where declarer wins the ♠A on the second round of the suit and leads the ♠9 to the ♠K, diagrammed below, is interesting because after the heart force, dummy’s remaining ♠10 is higher than East’s ♠8 but lacking an entry to dummy, declarer is still doomed.
Alternatively, declarer can take the ♥A on the first round. This just makes the defense easier. Later West’s second heart honor effects the anti-finesse force.
If declarer wins trick two with the ♠A he is still suffer the same fate after a spade to the ♠10 and ♠K, and a heart from East.
A club lead also works for the defense. The ♥J in dummy dooms a heart lead, whether high or low. A spade lead is also fatal for the defense because permits declarer to finesse trump a second time and then lead the ♠9. West can force to reach a position similar to the previous diagram but with the crucial difference that dummy still has the ♣A as an entry to pull the last trump. If East doubles 4♠ it will encourage the trump lead so it is just as well that most East’s avoided this temptation.
East’s ♠KQT8 is delicate. Reducing East to ♠KQT7 and putting the ♠8 in either declarer’s hand or dummy, keeping the suit 4-4, allows declarer to prevail on any lead.
There is passing similarity between the basic anti-finesse diagram above and the Devil’s Coup below. West’s trump ♠K looks safe because the trump finessing position has been destroyed. But if East is on lead, West is doomed.