Playing in an online game, my partner is as usual a bot. But then, so are my direct opponents at the table.
Nobody is vulnerable, and I pick up a 13 count, with 5 spades. As my mind wanders briefly into the pastures of whether this hand is worth an upgrade to 1NT, I see that while partner has passed in first seat, and that right-bot has opened 1♣. The hand is now only worth an overcall of 1♠ in my opinion, so I do so. When partner bids 1NT, all pass since I cannot see taking another bid.
Since partner won the bid, I am now declarer in the North seat, so these are the hands:
East bot leads the club king, as BBO moves me to the North seat to play the hand. It looks like I can probably find roughly 8 tricks in 1NT, but doing well at match points means I need to look for more. Diamonds is a suit I need to develop, so I start doing so at trick 2, with a low diamond to the 9. East wins the jack, then cashes the ♣QJ. West follows suit to the second round of clubs, but then tosses the diamond 3 on the third round.
Now, East exits with the diamond king. What is happening? East is a bot, one who does not know if North holds the diamond ace. But since East is a bot, IF north does hold the diamond ace, and East started with the doubleton KJ of diamonds, then East assumes I will "know" to cash the ace to drop the now stiff king. This is basic bot psychology, something that results from the use of double dummy engines to play the hands. That means the lead of a now stiff diamond king here makes sense. If North does not have the ace or queen, then exiting with the king now gets out of the way for West to win a later diamond trick. And if North has both the ace and queen, then the bot assumes declarer will know to drop a stiff king offside, so leading the king costs nothing in any case.
Conversely, if East has Kx(x) remaining in diamonds, then East bot will see the king as a likely entry, and may decide to set up the long club winner that I know it holds. This makes me think that East has started with KJ in diamonds, plus the known KQJ76 in clubs. What else does East hold in terms of points. 10 points are slightly too light for an opening bid, and there are 3 major suit honors missing, the ♠Q, and the ♡KJ. It looks like East has 6 cards in the majors, and needs one of the missing queen and king, but probably not both. With both, East may have chosen to open 1NT, well, at least if East was balanced. Given 6 cards in the majors, does East have shortness? East opened the bidding with 1♣, with I think 6 cards in the majors. If there is a stiff in one of them, they held 5 cards in the other major. I think then East would have chosen to open one of the major. So East is most likely semi-balanced, perhaps 3325, 4225 or 2425, but did NOT open 1NT.
Next, does East hold the heart king, but not the spade queen? With both red kings, I would be willing to bet that East would clear the club suit, setting up along club, hoping for an entry with a red king. Only a defender who lacks side suit entries decides not to bother setting up winners in a long suit against notrump contracts.
All of this is leading me to a nice picture of the East hand. 3325, 2425, 4225 shape. An opening bid, but not the ♡K, so probably the ♠Q to get to opening values. I don't know about the ♡J.
There are two lines I should consider now. I can cash the minor suit winners in dummy, then run the spade jack through East. If East covers, I can cash the top spades, then exit with the 9. If I've manage to strip the West hand, AND West is forced to win the last spade with the 10, then I'll have managed an end play, forcing West to lead away from the ♡K. This risks the possibility that East has started with QTx(x) in spades, so naturally covers the jack. That will put East in with the spade 10, and a long club. Anyway, even if I do manage to set up the spades, I'll then not have an entry to those spade winners.
Better seems to be to exit immediately with a low heart from the North hand. If you see where I am going with this, I am actually looking for an intra-finesse position. As expected, East does not play an honor, and certainly does not jump up with the king. So on the play of the heart 5, I insert the 9. This forces the jack from West, who exits with the diamond 4 spot. Queen from North, then East commits larceny, stealing my chance for an intra-finesse. East pitches the heart 10! Yes, East is probably worried about an impending squeeze.
Of course now the rest of the tricks are mine. Cash the other diamond, the club 10, pitching spade losers. Come to the South hand with two top spades. North remains with the A8 in hearts, South with the Q4, and I know the heart king is in the slot. Just lead the queen, and regardless of whether West covers of not, I will win the last two tricks.
So it WOULD have been an intra-finesse, but I felt cheated of the opportunity. Making 9 tricks was a good score, but I'd have traded that 92.9% score for the opportunity to smother the heart 10 when I led the queen.
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