"For those four who played in this game, they showed outstanding character and professionalism and were an integral part of the win," said Howley.
"They were told earlier in the week - each player at a different time - so they could focus on the preparation and I have huge respect for these guys.
"It was entirely my decision, I didn't discuss it with Warren [Gatland], and it was the hardest thing I have had to do as a coach, in particular for Dan Biggar. It is not a reflection on Dan's form and over the last four months he has played particularly well for the Ospreys.
"James (Hook) is adept at playing at 12 and 10 and is a hugely talented player. His kicking was exceptional and his composure was fantastic under pressure today."
Howley was pleased his younger charges gained experience against a top class outfit.
"Players like Harry Robinson, Justin Tipuric and Rhodri Jones had a good amount of top-level rugby today and that will be invaluable in terms of their development," he explained.
"Harry has pace and the ability to beat his man, he ran hard and every time he had the ball in his hands the crowd really reacted. He will learn and be better for this experience.
"What has been created since the World Cup is competition for places and we are delighted to have come through a highly competitive game without any major injuries - that is huge for us.
"In the Australia team we will be facing one of the best sides in the world and we are in good shape to challenge them in the test series over the next few weeks.
Howley added: "It was a Test match and we played like it. It was a huge squad effort this week. It wasn't pretty, there was a lot of turnover ball, but there's a lot we can work on in Australia.
"We're looking forward to it, it will be a momentous occasion next Saturday and we'll be going out there with every effort."