The Crystal Palace youngster made his debut as a substitute in Friday's victory over Scotland but was handed his first start in Swansea by Chris Coleman, though his team could not hold onto the lead provided by Gareth Bale.
"It was an unbelievable experience to play alongside the likes of Bale and Craig Bellamy," Williams told Sky Sports after the game.
|80/1||Wales are 80/1 with Paddy Power to qualify for World Cup 2014
Late goals from Dejan Lovren and Eduardo cancelled out Bale's opener to earn all three points for the visitors but Williams is still satisfied with the progress made over the international break.
"I think three points in two games is not bad," he opined. "Not many people expected us to beat Croatia but we came close and gave them a good game.
"It shows we're coming through as a team and improving every game."
The hosts worked hard to handle large periods of Croatian possession throughout the game and were close to a famous victory only for Igor Stimac's side to finally break their resistance in the 77th minute.
"It was a hard night," Williams conceded. "I thought we played really well first half. It's a shame we couldn't take that into the second half.
"When you're playing against the likes of Luka Modric, they're going to be good, they're going to keep possession and they came onto to us in the second half. We had to put the work in but you can't fault the lads' effort."
The victory keeps Croatia level on points with Belgium at the top of Group A and leaves Wales in fourth place battling with Serbia for third place in the group.