In a no trump contract there is always a race to establish their own respective suits between the declarer and the opponents. Whosever gains in taking the initiative ends up a winner, if there are sufficient entries to run that suit. At times the play requires perfect timing and at the same time declarer is always on the lookout for any adverse distribution that could spell the death knell for him as illustrated in our hand for today where south is in 3NT on the following bidding and hand:
The bidding:
The opening lead by west is however not a heart, but the 7S. As south, how do you play 3NT?
On close analysis, you know that on east's heart overall, it is most likely that both the black kings lie with him. West's failure to lead a heart perhaps places him with either no heart or at the most a singleton. You can also fathom that the opening spade lead has been a bit favourable for you giving you 2 spade tricks placing the KS with east. A count of tricks now gives you 2 spade tricks, 2 hearts, 2 diamonds and one club for 7 sure tricks. You need therefore, to find two more to enable you to make 9 tricks in 3NT. The question is where do the lie? After east plays the KS taken by you with AS, you ponder over the club suit as your best chance, with the next best alternate being the diamond J finesse and the break of the suit 3-3.
In Bridge the safety factor is top priority. The club finesse is most likely to fail and if so it also goes in to the danger hand form where a spade return would establish west's 5 card spade suit. So how best do you take care of these lurking dangers?
Did you take a club finesse? No! Well done. You played to the ace of clubs and voila! The KC singleton drops you now have 8 tricks, which is good but still not enough. There is more to come. Of course when you led a club you had 3 considerations. One, if west plays the king, you let it hold to avoid the lead going into the danger hand east. Two, if west plays low and KC does not fall under the ace you intend to return a low club from dummy keeping the JX and KX factor with west doubleton, which would again, suit you fine as west on lead could do no damage. Finally if west held KJ109, even he could be held to only two tricks.
Well proceeding in the play, after the drop of KC under the ace, declarer returned the low club to ensure three club tricks, which would give him the 9 tricks needed. Here the point to remember is that giving up a trick early always puts you in command. Supposing the trump suit is distributed in this way.
To lay down the ace would be disastrous. The safety play demands a duck in the first place to curb west running away with the suit. In Bridge the most essential rule to keep in mind is: Safety first.

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North       South
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   32        AQ10
 A109         K32
  A43        KJ52
AQ542         763
=================

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W        N        E        S
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P       1C       1H      3NT
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                    All Pass
============================

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XXX
KJ10X        X
AQXXX
============================