Problem

The Auction:

West   North   East   South
                                 1♠
pass     2♠       pass    4♠
all pass

You are South on this deal in a pair event, where the objective is to take as many tricks as possible, playing against expert opponents. West leads the ♥3, you call for dummy's ♥10 and ruff East's ♥A. While there are several reasonable lines of play at this stage, say you choose to cash the ♠A and play a spade towards dummy's queen, which wins as East discard a heart. When you run the ♦Q, West follows with the ♦10. Plan the rest of the play.

Solution

After West follows with the ♦10 when you run the ♦Q, the automatic continuation is to run the ♦J. If you do so, the roof caves in, for West unexpectedly wins the ♦K, cashes the ♠K and exits with yet another king, the ♥K to lock you in hand. Unable to take club finesse anymore, you can take no more than ten tricks.

Once the ♦Q wins, a little foresight will point out that the winning play is to play a diamond to the nine! As the cards lie, West will win the ♦K, but you have the ♦J as a dummy entry to take the club finesse. If the ♦10 is indeed a singleton, then whether West ruffs in or not, you can arrange to ruff a diamond in dummy to establish the fifth diamond as a winner, and in the process gain an entry to dummy to take the club finesse. Furthermore, if the ♦10 is singleton, you need to ruff a diamond in dummy even if you play the ♦J from dummy, so playing a diamond to the nine is a no-risk play. Finally, if West played the ♦10 holding a doubleton, playing a diamond to the 9 is once again equivalent to running the ♦J.

Par Contract Analysis

The par contract on this deal is 5♠ by North-South.