King says Crystal Palace stopper Wayne Hennessey was also culpable.
Wales have failed in their bid to reach next summer's World Cup, losing a crucial qualifying match to Ireland.
Williams took plenty of flak on social media, but former Premier League defender Ledley King spoke up to say that he felt the criticism of the centre-back was too harsh.
He pointed his finger at Wales and Crystal Palace goalkeeper Wayne Hennessey for his role in the game's decisive moment.
I see a lot of tweets about Ashley Williams no doubt he can do better but the keeper needs to take responsibility for a poor decision imo.— Ledley King (@LedleyKing) October 9, 2017
The match was a game Wales could not afford to lose, and it will not help William's confidence after a poor start to the season at club level - and the same can be said of Hennessey.
Ireland are not yet guaranteed a place at Russia 2018 as they must negotiate a play-off tie after Serbia sealed qualification from Group D as winners, two points ahead of Ireland.
Wales finished two points further back and will be left wondering whether the result would have been different if they had the injured Gareth Bale available.