Twelve months after suffering a stunning defeat to Neil Robertson, who needed two fouls to recover from 67-26 down in the deciding frame, Williams made sure there was no question of a repeat with a clinical performance.
Williams dominated on the safeties and punished errors from Lisowski to seize the upper hand, and said his performance shows he is over the disappointment of last year.
"I'm enjoying it, I'm in another final, especially after last year," he said on Eurosport. "A lot of people said, 'How would you get over that?' As soon as I walked out I was over it and I'm back in the final now.
"It's easy to win but when you lose you have to get over it. I've never been worried. If I lost 6-5 from 5-0 up, it wouldn't have made any difference. I would have said, 'best of luck Jack' and move on."
It means the world number seven is into his first final at the Alexandra Palace - with The Masters still at the Wembley Conference Centre the last time he made it to the last two.
Williams will now face Judd Trump, who overcame Stuart Bingham 6-1 in the second semi-final.
Trump went 4-1 up when he edged a tense fifth frame which lasted some 45 minutes. As it came down to the colours, Bingham sank the green with a full length double but then missed on the blue, allowing Trump to come in to nick it.
Trump wobbled again in the sixth frame but Bingham could not take full advantage and soon fell 5-1 behind.
It looked all over as Trump moved into a 58-0 lead at the start of the seventh, but a missed red opened the door again for Bingham, who got within 29 points before another safety battle began.
Both players were guilty of fouls but after Trump potted a tough yellow, he put the match to bed.
"It was a struggle at the end but I felt good, I felt a lot better," Trump said. "The first three or four frames I went into it a few times but didn't finish on anything.
"I need to make a century or a big break to settle me down. It didn't really run and I felt like I was making chances. It was a bit scrappy in the end but I managed to get there."