Source: Gerben’s Bridge Blog Wednesday, September 27, 2006       

So when do you underlead an Ace in a trump contract? The first rule you learn is: Never!

Here are some things that could go wrong:

* An opponent could win a trick with the King he would otherwise not get.
* Even if partner has the King, this might not gain a trick.
* Partner has the King and it would gain a trick, if only he knew to put it in. He expects declarer to have the Ace and will play accordingly!
* Partner has the Queen, the King is in dummy and declarer plays small and STILL it won’t work, for example:

K 10 3
A 8 7 5 Q 9 4
J 6 2

On the lead of the 5, dummy plays the 3. Now East will correctly put in the 9!

This was just a short list of horrible things waiting to happen to someone who underleads an Ace. But… as always there are exceptions.

Against a slam with a void

(1) 2 (3) 3
(4NT*) Pass (5 – 1 KC) Pass
(6) All Pass

You’re on lead with:   AJT743   432   8432  

Now the correct lead is the 3! We are likely to make exactly 1 Spade trick (declarer is not void because of Blackwood) so a ruff seems like the only possible way to beat it. We must hope partner has the King and then returns a Club to beat the contract.

Their contract will likely make and declarer has no control in the suit.

The opponents bid unopposed:

1 2 (GF)
3 (extras) 4 (non-serious cuebid)
4 Pass

Now if you know that they would cuebid a singleton in opener’s suit you may consider leading a  or  away from Axx. This is safer than usual since partner will know you have the Ace, but declarer will not. The lead away from A loses some of its attraction if declarer can have a singleton Spade though.