Posted 2012-May-22, 23:18
If partner has the ten, and you play the 9, you will probably make 2 tricks. Declarer will finesse partner for the queen (I can tell you why if you want), and you will make partner's long ten as well as your queen.
If partner has the ten, and you play the queen, you will only make 1 trick (declarer will play off A, K, J and see if they are 3-3).
If partner has the king and you play the 9, you will make either 1 trick (if declarer plays the ace next, then low to the jack), or 2 (if declarer thinks partner started with KQxx, and you with T9 doubleton). 2 is unlikely (partner might put in an honour when a card gets led towards the AJ, in case declarer started with only 2 cards, then he can't lead towards the jack again. Declarer knows this, so it's less likely he started with KQxx if he doesn't put in an honour).
If partner has the king and you play the queen, now declarer has a solid finesse position against the remaining honour (he can lead the ten, squashing your 9 - he has the jack and the ace to take care of partner's king and 8). So you take only 1 trick.
In both cases, if you play the queen you are guaranteeing only 1 trick. Whereas playing the 9 might get you 2 and definitely at least 1. Therefore play the 9.
I ♦ Transfers