In his prime, the late Jim Jacoby had few peers as a declarer. This deal comes from the team trials in 1965 to select an ACBL representative to the 1966 world championships.
West led the ♠K, followed by the ♠A and a third spade. East ruffed and returned a diamond.
Jacoby won in hand and, analyzing the deal perfectly, came up with the only successful line of play.
Jacoby played a low heart from hand and inserted the 7. Next came the ♥A and a heart to the king. The third round of trumps simultaneously picked up the opponents hearts and squeezed East, who had already thrown two clubs on the first two rounds of hearts.
If East discarded another club on the third round of hearts, Jacoby could ruff two clubs in dummy, felling the ace, getting back to hand twice with a high diamond and a diamond ruff. If East discarded a diamond instead of a club on the third round of hearts, Jacoby would cash the high diamond in his hand, ruff a club to dummy and ruff out the ♦J, getting back with a second club ruff.
The low trump from hand a trick five was necessary because Jacoby needed to be in his hand – not dummy – on the third round of trumps.
The full deal: