See if you can defend better than one of my ACBL Bulletin colleagues did. This deal was from the 2018 Spingold semifinal. West held:

 A752  
 KQJ106  
 A  
 K73.

With both sides vulnerable, his partner opened 2 (!) in second seat. In this position, partner should have a good hand, so slam is definitely in the picture. RHO overcalled 2 and our (anti)hero cuebid 3. LHO bid 4. When a passed hand comes in with a new suit at a high level, it should promise support (spades); it can't be only diamonds or he would have preempted in diamonds initially. Opener bid 4, RHO bid 4 and my colleague jumped to 6. This was passed around to the overcaller who now tried 6, doubled and passed out. What would you lead?

Vul:Both Dir: North	983  7  KJ876  Q1065
A752  KQJ106  A  K73

Expecting the declarer to be able to set up diamonds, a low club was selected. Dummy played low and partner won the A and returned a low club to the 9 and king. Now what?

With partner likely to have the A, I would think West should be trying to get a diamond ruff. He can cash the A and then play a heart to get a ruff. Which heart? Something to make sure partner wins--like the Q. Partner will think declarer has the K, so will win the ace and see no other choice but to issue a diamond ruff for down 5 (1,400 in the form of 2 clubs, 1 in each major, the A and a diamond ruff).

This was the Real Deal:

Vul:Both Dlr: North	983  7  KJ876  Q1065
A752  KQJ106  A  K73		--  A98432  532  AJ82
	KQJ1064  5  Q1094  94

Notice how turned on South was by North's thoughtful 4 call. Personally, I think East's hand is too good for a 2 preempt (3 first-round controls!). Anyway, the other East-West pair reached 6 and made 1460. My ACBL bulletin colleague failed to find the winning defense. After winning the K, he played the K next (killing partner's entry for the diamond ruff). Defeating the contract only 1100 lost 8 IMPs. Down 1400 would have been a loss of only 2 IMPs (and down 1700--available by getting 2 diamond ruffs would have been a gain of 6 IMPs). The team on the losing end of this swing lost the match by only 2 IMPs. Taking just one more trick on defense would have landed them in the Spingold final!