The Power led by a solitary point at half time, but threatened to blow the tight contest wide open with four unanswered goals in the third term.
Utility Tom Logan had a chance to put the home side 23 points up with a shot on goal late in the quarter, but missed and the momentum swung the Blues’ way.
The visitors kicked eight of the next nine goals to set up the 26-point win and post-match Williams described the game as the one that got away.
“I thought that we dominated the play in the first part of the game and couldn’t get any scoreboard pressure on" he said.
"It was 23 minutes and 50 seconds into the third quarter when Tommy Logan had a shot on goal to put us four goals up, but he missed and they scored after that quite heavily for the rest of the quarter,” Williams said.
“You have to be ready to finish off the game when the opportunity comes. We had an opportunity to do that and we didn’t do it.”
Port Adelaide had earned a reputation as final-quarter specialists, after coming from behind to win on four separate occasions this season.
The Power also had the added bonus of an extra two-days break over the Blues, who were further depleted by the loss of emerging midfielder Kane Lucas (hamstring) in the first quarter.
Williams said he couldn’t explain why Carlton was able to finish the game the better of the two sides.
“Given the circumstances of us hitting the front, at home and (the fact) that we had more days break I have to say that Carlton should be very proud of their efforts,” he said.
“It was a game, that after being in that position, we would win most of the time. It certainly felt like we let that go and Carlton grabbed it out of our hands. They showed a lot of resilience.”
