South ruffed the club continuation, cashed three hearts discarding a spade and unblocked the ace of spades. He proceeded with a crossruff to emerge with twelve tricks, N-S +420.
The overtrick was important since there are very likely only nine tricks available in 3NT (+400).
North was faced with a bidding problem when partner responded one spade. He was not strong enough to reverse and elected to underbid with 1NT. He came to life with a jump raise of diamonds and the excellent minor suit game was duly reached.
Some players would open one diamond with a club rebid available when partner responds in spades but this action does not tell the truth about his minor suit length. There is some danger of play in a 4-2 diamond fit when South offers a preference.
The other option would be to open 1NT with the singleton ace of spades. The ACBL has recently changed the laws so that a player may do so with a singleton ace, king or queen. This call runs the risk of playing in a spade contract when partner employs a Jacoby or Texas transfer and, therefore, in my opinion, has no appeal.