You are in three diamonds (both vul) as South. North had a difficult decision after West’s preempt and reasonably chose to respond three diamonds. That’s where the bidding ended:
West led the ace of spades, South playing the Jack and you the six (trying to hide the spade situation from West). West continued with a low spade and East ruffed with the six of diamonds.
At trick 3 East shifts to the nine of hearts. You play the jack and it wins as West follows with the deuce.
At trick 4 you lead the deuce of diamonds, West discards a low spade, you play the king and East plays a low diamond. How many diamonds did East start with? It does not look like you will make the contract. What do you do now?
When I observed the hand, declarer did not get flummoxed. She reasoned that she needed to do as well or better than the other NS pairs. After all, diamonds were going to break 5-0 for all declarers. She managed to hold it to down one. Do you see how?
She had lost one spade, one spade ruff, and was sure to lose two more diamonds. If she could hold her club losers to one, she would get out for down 1. It was likely that East held the club ace, so if she could endplay East, the ace would be her only club loser.
At tricks five and six she cashed her two top hearts ending in hand. Then she led a low spade ruffed with dummy’s and overruffed with East’s nine. At trick eight East led the diamond queen taken with declarer’s ace. At trick nine she led the king of spades, but East could see the endplay coming and refused to ruff. Declarer then led a trump to East’s winner and the endplay was complete, resulting in 75 percent of the matchpoints for NS.
Here is the entire hand:
You may want to lay out the hand with cards on the table to make sure you follow it all.
BTW, West erred in leading the ace of spades. Any other lead and South will go down two. Some declarers went down three, failing to make the endplay.