Giggs picked Anderlecht centre-back James Lawrence before this 34-year-old, who arrived for the last 17 minutes of Sunday’s 1-0 victory.
Gareth Bale led Wales in Williams’ lack but Giggs denied that has been a permanent switch.
“No, Ash stays the captain. You are never going to shoot it well,” he said.
“He did not sulk. That you never need players to choose it well. You’ve seen that which he brought when he came – the leadership qualities”
“That has been the sole real reason. We gave him 60 moments [in Wednesday’s friendly win over Trinidad and Tobago] and I wasn’t too sure until yesterday.
“It wasn’t an instance of ruthlessness. It was trying to select the ideal team and having the team .
“It was the only position where I was deliberating. He arrived, saw us home and is part of these plans going forward.”
Williams’frustrated and disappointed’
“It is obviously disappointing to not play but it’s about being ready if you are required to conquer the lineup,” said Williams.
“He said [your choice ], he’s the manager and he makes the decisions. Clearly I would love to engage in and it’s frustrating but he’s the manager and you go with it.”
Even though Williams was frustrated to not begin, Giggs believes he played an important role as Wales devoting late Slovakian pressure to win on Sunday.
“getting into the week I wanted two sheets that are clean,” he said.
“Without Chris Gunter [against Trinidad and Tobago] that does not happen.
“If you are older you can even learn from the younger players. We have talented young players but we can not do it without the experienced players.
“Plus it’s not easy leaving those professional players it’s not easy in any respect.”
‘The perfect beginning’
Sunday’s win over Slovakia has been a significant one for Wales, that are intending to qualify for an additional successive European Championship but only a third key championship within his or her own history.
Giggs’ side, that will be the 2nd seeds in Group E, took the lead inside five minutes because of Daniel James’ fine strike however they lived dangerously in the closing stages.
Wales defended stoutly to concentrate to that which could prove to be a crucial win against Slovakia, the band’s third seeds and potentially their closest competitions for a few of those two automatic qualifying places.
“It was the ideal beginning really.
“There was a bit of pressure on people. I tried to play down it but you can not hide from the truth that the different teams have played that Croatia and Slovakia got three points.
“We all will study from today because we were placed under some great pressure at the ending. I contested that the players to keep more sterile sheets because we all feel together with our assaulting ability we’re going to create opportunities, we’re likely to score goals.
“It is going to ensure it is more essential that people keep clean sheets”