Don't be careless

Here's is another IPBA deal. Playing matchpoints, you bid to 6NT on this:

                ♠ Q 10 8
                ♥ 10 8
                ♦ 8 7 6 4
                ♣ 8 7 6 5
♠ 9 7 6 4 2                  ♠ ---
♥ J 4 2                      ♥ Q 9 7 6 5 3
♦ 3                          ♦ K 9 5 2
♣ Q J 10 2                   ♣ 9 4 3
                ♠ A K J 5 3
                ♥ A K
                ♦ A Q J 10
                ♣ A K

You open a strong 2♣ bid, and North bids 2♦. You rebid 2♠ and North raises to 4♠, weaker than 3♠. Over 4NT, Keycard Blackwood, North shows no key cards, but you ask and he shows he has the ♠Q, but no king. You sign off in 6NT.

West leads the ♣Q and you win the king. My first thought would be why can't I hold hands like this playing rubber bridge for money? You've done well to play slam in notrump instead of spades. You see that you can concede the ♦K and claim 12 tricks, but (because it's matchpoints) can you take all 13 tricks if the diamond finesse works?

You should start with the ♠J. When West follows, it's safe to overtake with dummy's queen. You lead a diamond to the queen which holds. Now, you have two more entries to dummy to repeat the diamond finesse. You lead a low spade to the 8, and later a spade to the 10.

What if you are careless the first time you go to dummy? Suppose you lead the ♠3 to the 10 and take one diamond finesse. But now, when you lead the ♠5 towards the ♠Q 8, an alert West can play the ♠9, and you don't have enough entries in the situation as shown. Actually, it's not hard for him to find that play, is it?

Here is the same deal with the Handviewer from BBO:



You can click "next" to follow the card play. Which one do you like better?