The best South could do was to discard a spade loser.

Thanks to the even split, he was able to discard his spade loser.

If South has a singleton club, he will still have a spade loser.

He knew that South had bid the slam with two or three quick spade losers.

There were two chances to avoid spade losers and the first of them failed.

Now he has allowed South to make his contract, converting two spade losers into one.

Now it was a question of whether a spade loser could be avoided.

South would be unable, at the end of the day, to avoid a spade loser.

That would set up the clubs to take care of the potential spade loser.

South must then find a way to discard a spade loser on a red winner.