Mowbray, who compared Williams to a Rolls Royce, feels the former Burnley loanee slotted straight back in to his line-up and is thrilled to have his services at his disposal once again.
"It was great to see Rhys Williams back after being out for four months," Mowbray told the club's official website.
"He's only had a week's training and has played 60 minutes of a youth team training game.
"I didn't have any thoughts of putting him in the 18 yesterday but I changed my mind at the death.
"Rhys brings great versatility and quality to our squad and he's going to be like a new player for us coming back for the second half of the season.
"It was a good thing for him to get 45 minutes under his belt. Rhys never seems to over-exert himself. He has great quality and I've said in the past that he's like a Rolls Royce.
"We can use him in so many positions so it's like more than one player coming back because he's three players in one."