After my ♠A lead, I decided on one of two lines:
1. Play another spade and give partner a ruff if that 3 was a singleton.
2. Play my singleton club and hope partner has the ace and gives me a ruff.
I was wary about playing a club because if partner doesn't have the ace, it could give a trick away if partner has a couple of club honors, so decided to cash my ace and see what happened. What happened is I hit the one layout I didn't want when my partner's queen came down, establishing the jack in dummy. Having still convinced myself a club lead is dangerous, I decided to lead a third spade to neutralise dummy's jack. Unfortunately when partner ruffed low, declarer picks up the suit for no losers and makes the contract, the other two pairs managed to get it off.
I can't seem to stop myself from doing cock-ups like this . I wish Dealmaster had defense hands as well as declarer play, then I might be able to train myself to work things out better and use all information available.