I have been heavily critisized by my team-mates for a defensive play which they decidingly judged as an error that only a beginner could make. We were playing IMPs, against opponents unknown to me. I led the ♦A, and, on my partner's encouraging high spot, the nine, I continued with the ♦K. With dummy's menacing club suit, I was clearly in a cash-out situation. It remainded to spot where our winners were. I decided to believe partner and played my last diamond - ruffed by declarer.
They said I ougth to know that the ♥A was with East: South would not simply jump to game holding a side ace, they argued, and partner did overcall in hearts. On the other side, I reasoned, our fourth trick could well be a natural trump trick, if only East had any singleton spade honour, in which case I had hurridly to play a diamond to partner's queen.
Was my reasoning so faulty? Shouldn't my partner give me a discouraging signal, since he could see that declared held two diamond cards (from bare AK, we lead the king)?