Hands are from Soledad Club, October 8, 2018.
South (Dummy): ♠Q6 ♥A109763 ♦K98 ♣A10
West: ♠K1032 ♥QJ5 ♦J1043 ♣52
This hand is interesting for the defenders. You and your partner pass throughout. North opens 1♣ and South responds 1♥. The auction continues 2♣ 2♦; 3♦ 3♥; 3NT by North. According to this bidding, declarer should have six clubs and four diamonds. The only question is whether she has three spades and a void in hearts or two spades and a heart singleton.
Partner leads the ♠9. This is clearly top of nothing, so the ♠A and ♠J are behind you in Declarer's hand (with the doubleton ♠Q visible in Dummy). However, you and your partner lead small from ANY 5 cards in no trump, even with no honors, so you know that partner has only four spades, which leaves Declarer with three spades and zero hearts.
Declarer plays low and you encourage with the ♠3 as Declarer takes the ♠J. She plays a club to the ♣A on Dummy and runs the ♣10 to partner’s the ♣Q. Partner continues with the ♠8, ♠Q from Dummy, ♠K from you and ♠A from Declarer.
Now Declarer reels off four more club tricks, discarding hearts from Dummy. What do you discard?
It should be clear that you have sole responsibility for guarding the diamonds. Declarer has announced four cards in the suit and you have four with Dummy holding three. Your partner has a doubleton diamond. So, you must keep ALL your diamonds. You must also keep ONE heart honor to help your partner out, but you can come down to the singleton the ♥Q. So, your discards should be the ♠10 and the ♠2 followed by the ♥5 and the ♥J.
Partner with ♥Kxxx, expects to guard hearts, but should also know that Declarer is void in hearts so can come down to ♥Kx of hearts, discarding two hearts and one diamonds on the run of the clubs. [If partner has not divined the heart void in Declarer's hand, she can discard one spade and keep three hearts.]
Declarer can go to Dummy with the ♦K and cash the ♥A, discarding a losing spade. Then, when she plays the ♦8 from Dummy, you cover with the ♦10 to ensure she is stuck in her hand. She will have to give you the fourth round of diamonds and make only 11 tricks.
Double-Dummy play (by Deep Finesse) makes seven on the hand by finessing the clubs the other way, picking off your partner's ♣Q. Deep Finesse will also take the spade finesse, AND finesse you for both the ♦J AND the ♦10 (running the ♦8 and then the ♦9 from Dummy to promote the ♦7 in the North hand if you cover). No human will do that in real life, so don't feel guilty for not making seven on the hand!
Repeat the Mantra after me: Slams are based on TRICKS (e.g., long, good suits) and controls (lots of Aces and Kings).
South: ♠AK96532 ♥76 ♦82 ♣107
North: ♠QJ ♥K53 ♦AKQ10953 ♣A
Everyone SHOULD have gotten to slam on this hand—the only question is which denomination. East passes and South opens 3♠. North, with first and second round controls in all the other suits and a fabulous SOT (Source of Tricks) diamond suit, simply jumps to 4NT (which agrees to spades). Upon hearing 5♥ (two Key Cards with the Queen), North has to decide between 6♠ and 6NT.
6♠ will be slightly safer if partner has a void in diamonds and has to do some ruffing to set up the suit. Ditto if partner has a singleton diamond and diamonds break 4-1 with ♦Jxxx in one hand. On the other hand, as long as partner has even ONE diamond, you are bringing seven diamond tricks to the table 73% of the time, the sum of any 3-2 (68%) and the stiff jack (5%).
6NT has two huge advantages: (1) it “right-sides” the contract and protects your ♥K from the opening lead—in case the ♥A is behind you. (2) it is a better score in matchpoints.
I believe that the odds favor 6NT over 6♠ for both safety and payoff in terms of scoring.
I am sad to report that of the 14 pairs who played this board, only one pair bid 6NT. Three pairs bid 6♠, but one went down because he forgot to pull a third round of trumps before trying to run the diamonds. Of the other two pairs in 6♠, one made only six because the ♥A was cashed at trick one and the other made seven—lead other than the ♥A. One pair was in 4♦ making six. One pair was in diamonds only making five. One pair managed to make only five spades. Seven pairs were in game, make seven.
This hand again emphasizes the importance of recognizing that good, long suits make slams! North should expect six or seven diamonds tricks from that suit. When partner preempts 3♠ and you have the filling Queen and Jack, you should expect seven tricks from your partner's spade suit—unless your partner has a habit of making truly horrible preempts. This puts you in slam territory! Ask for Key Cards.