Posted 2011-March-31, 15:24
If our objective is to make:
A club to the jack works when clubs are 3-2 with the queen onside, or singleton queen onside, or Qxxx onside but the spades coming in. Ignoring inferences from the lead, that's about 34 + 3 + 6 = 43%.
Playing spades from the top works when spades come in, and either ♣Q comes down in two or LHO has ♦A. That's about 52 x (0.5 x (2/5 x 0.68 + 1/5 x 0.28) + 0.5) ~= 35%. However, you also survive when spades don't come in but there's a singleton queen of clubs on the left, so that gets us up to about 36%.
At IMPs, a club to the jack is clearly best.
Considering the matchpoint problem:
If the club finesse works, we may then find the spades coming in too, and make 11 tricks. Or if spades are xx-Jxxx offside but LHO has ♦A, we will still make at least 10 tricks. If the club finesse loses, we lose a club, probably four hearts, and a diamond for two off.
If the spade line works, we might get one overtrick if LHO has the red aces and ♦J (cash the spades, cash two top clubs, lead ♦Q), but two overtricks will need everything working. If the spade line fails, we lose two black-suit tricks.
So a club to the jack is still better than playing spades.
Playing for one off might be reasonable if we had a good line for one off, but we don't.
Hence a club to the jack is best at matchpoints too.
... that would still not be conclusive proof, before someone wants to explain that to me as well as if I was a 5 year-old. - gwnn