The 48-year-old moved one victory away from becoming the oldest winner of this Triple Crown event with four half-century breaks enough to down old rival Murphy in their first meeting for five years.
Murphy reeled off two superb three-figure breaks, including 131 in the third frame, but O'Sullivan's cavalier approach paid dividends with reds aplenty potted in this semi-final to delight a packed Alexandra Palace crowd.
"I don't feel that old," O'Sullivan, the youngest ever Masters winner, told BBC.
"I know my age but I feel young in my mind and I feel young when I am around the table.
"I feel a lot younger round the table than I do when I play these young players. They look old! Their brains are quite slow so for me, I feel like my brain is pretty quick around the snooker table, which is enough.
"Yeah, they need to get their act together because I am going blind, I have a dodgy arm and bad knees. And they still can't beat me!"
O'Sullivan had bemoaned his standard and the "disgusting" Alexandra Palace venue after Thursday's last-eight success over Barry Hawkins and started this encounter by potting the white.
It was not a sign of things to come as the seven-time Masters champion won a nip-and-tuck opener.
Murphy, who had been working beyond midnight for BBC's commentary team on Friday, missed a black in the second and O'Sullivan responded with a break of 52 to take a 2-0 lead.
It was already approaching now-or-never territory for Murphy, but he responded with a scintillating century in the third frame.
The 2015 champion cleaned up with a 131 break after a slice of luck with his final red to reduce the deficit.
After an error-strewn start to the fourth frame, O'Sullivan showed his class with a rapid 42 after several safety shots to earn a 3-1 advantage at the mid-session interval.
Murphy came out with renewed intent to send down his second hundred break and fourth of the tournament, but it only appeared to click O'Sullivan into gear.
He served up a quick-fire 90 before breaks of 71 and 62 put him on course for a record-extending eighth Masters title.
O'Sullivan added: "The start of the match, there were a few mistakes but I cleaned it up a little bit and I need to do that these days because I can't pot as well as these guys, but I can make good breaks amongst the balls and make up for it that way.
"So, yeah I played decent and won the match."
Murphy was gracious in defeat in the first Masters meeting between the pair.
"He was just too good, simple as that," Murphy said.
"I just thought Ronnie was superb and sure if he plays like that you may as well give him the trophy now."
In the final, O'Sullivan will meet Ali Carter, who beat Mark Allen 6-3 in Saturday's evening match.
After the second frame, play had been temporarily paused for around 10 minutes for a member of the crowd to receive medical attention before Carter made successive century breaks to lead 3-1 at the interval.
Another well-crafted 105 break extended Carter's lead at 4-1 before Allen stopped the run with a century of his own in the fifth frame. Allen then made it 4-3 after Carter had missed a red when looking set on a break of 55.
Carter, runner-up at the 2020 Masters, regrouped to take the next frame 87-8 before there was another brief pause in the ninth frame when a woman in the audience needed medical attention.
It was Carter, though, who kept his composure through a tense finale after both men missed chances before he cut a thin blue to the bottom corner before sealing victory on the pink.
