The 21-year-old had a hand in all four goals in Monday's 2-2 draw, opening the scoring against his old club before twice giving the ball away for the visitors to score.
His remarkable match continued when he deftly headed on for Michu to equalise after the interval but the midfielder was downbeat afterwards, saying sorry to the home fans for his display but Williams hailed Shelvey's character.
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|12/1||Jonjo Shelvey is 12/1 with Coral to open the scoring v Valencia
"He isn't shy, and I think for a 21-year-old to play how he plays anyway shows he has courage. He is always getting on the ball, he never shies away from it.
"I just said, 'Don't worry about it' to him. I know more than anyone what it's like to make a mistake so I wanted to get him to carry on with the game like normal.
"It happens, we all do that. The important thing is that he was always willing to get on the ball.
"Mistakes stick with you for a little while, but the good thing about football is you've always got a training session.
"The lads have already taken the Mickey out of Jonjo a little bit, but we've got a game Thursday and we've got a game Sunday.
"It won't stay with him for too long, but it hurts at the time."
Swansea will embark on their first match of the UEFA Europa League group stage with a trip to Valencia on Thursday.