This hand is from the 2016 Autumn Nationals Spring Pairs in Adelaide. The auction was straightforward but the play is quite difficult after the lead of the six of hearts to the nine and jack. You may like to stop here and decide how you would play it.
There are two obvious lines after winning the jack of hearts. Most declarers want to protect the king of hearts and see the reverse finesse in diamonds as their salvation. At trick two, they lead a diamond to the king and then return the jack. If East does not cover, the jack wins and if East does cover, the 10D is smothered at the same time. All these declarers were successful.
However, some declarers decided that the best chance of making the five diamond tricks required for the contract was to take a first round finesse of the jack of diamonds and these declarers all went down. The result on any one hand doesn’t actually tell you what the correct line is. So now you might consider whether the finesse or the smother is the correct line.
The way to make an analytical decision is to realise the diamonds must be 3-2 for both lines and to count how many cases are favourable for each line. The smother line requires West to have 10x which is three cases (108, 107 or 103). The finesse line works for Qx (same three cases) and for Qxx (six cases). Thus, the finesse is nine to three better than the smother line. Of course the preempt lessens the chances of West holding three cards but the requirement for the diamonds to be 3-2 offsets this.
So the finesse seems better because it offers nine tricks where the smother play has trouble finding nine tricks if it loses. Surprisingly, there is a third interesting line suggested by Kit Woolsey. Win the opening lead with the KH and play the smother line. When it loses, if West does not have the 10H, he is likely to play East for J109(x) of hearts and will underlead his heart so as to unblock the suit. It will be a nasty surprise when South turns up with the jack of hearts.