Easier for me to see

I played bridge online last night with Kate. I was West on this deal (rotated):

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

South opened 1♠, North bid 2♦ and South raised to 3♦. North rebid 3♠ and South raised to 4♠.

I led the ♥2 to the 6, 8 and jack. Declarer led a diamond to the king to advance the ♠J, won by my ♠K.

I could see there was no point in giving partner a diamond ruff (I had a natural trick in that suit), or so I thought. I shifted to a high club, declarer ruffed the second one and drew two more rounds of trumps. On the third spade, I discarded a low club. Here are the cards that were left:

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

Declarer led the ♦7 to my 8 and dummy's king. Do you see how declarer can make the contract? I could, but it was easier as a defender. If South leads a diamond to his ace, he can cash the last trump and I have to discard my ♣8. Now, declarer can exit with a diamond and I'm endplayed in the heart suit.

Declarer didn't do that and was set one trick. I was surprised later to run it through Deep Finesse and find that when I was in with the ♠K, a diamond return is the only play to guarantee setting the contract at that point.

For plus 100, we won 1.69 IMPs. Out of the 71 pairs who played North-South, only six bid and made 4♠. On opening lead, a diamond lead (or a club lead and a diamond shift) is the only way to legitimately set it.

You can see all the results if you click here.