John Higgins booked his place in the World Championship final after beating Stephen Maguire 17-15 at the Crucible.
Higgins braved unbelievably tense conditions to win through
Having been 14-10 down overnight, Higgins won the first three frames to reduce the deficit, aided by a 104 run that could have been a maximum break.
Maguire pulled one back before the mid-session interval, but a 122 clearance put Higgins back in touch.
And the 1998 champion came through the last three frames under huge pressure to complete a stunning turn-around.
It was a remarkable session, to follow three quality sessions before it, and Maguire was left only to applaud Higgins play after a gargantuan effort.
Higgins started the session in ominous form, knocking in breaks of 41 and then 104, before runs of 36 and 39 in the 27th frame brought him to within one frame.
A topsy-turvy 28th frame went Maguire's way, though, to ensure he went into the mid-session interval as favourite - but Higgins' experience told after the break as he mixed fine breaks with top safety, and large slices of fortune, to come through.
A fabulous 122 reduced Higgins' deficit once again in frame 30, before Maguire battled brilliantly to gain the initiative in frame 31 - only for the 26-year-old to miss frame-ball pink and allow Higgins to level.
The final two frames were wrought with errors and missed pots as the pressure told on both players, but Higgins snatched both to gain victory and a place in the showpiece final.
I think giving up the booze has helped me with my game
"I'll be honest, it was absolutely mad out there, especially in the last frame. But I'm just so delighted to win," an emotional Higgins said after the match.
"I've never fought so hard to come through a match in my life. I was just hanging onto Stephen's coat-tails for most of the match because he was playing so well, making unbelievable pots.
"I never thought, even at 14-10 down, that I was out of it and I've been working on my positive thinking and relaxation exercises to deal with situations like this."
Higgins admitted his decision to stop drinking alcohol had helped him rediscover form after a spell in the doldrums.
"I think giving up the booze has helped me with my game. I just used to go out and enjoy myself and not practice for a few weeks," he said.
I may never have another chance like this
"I do enjoy a drink but the problem is I don't know when to stop sometimes if I am out having a few drinks. I'm glad I don't touch it now - I just think I practice more.
"The weekends were all about going for a few drinks after watching Celtic and going to a club afterwards so I was never practising at weekends.
"When you've got a hangover, you don't feel as if you are really over it for a day or two so it was eating into my practice time and I was turning up still not feeling right.
"Now I am practising more. That maybe is the reason I am playing a bit better. I also feel a lot more healthy."
Meanwhile, Maguire was distraught after seeing Higgins overcome the four-frame deficit.
"I am absolutely numb. I threw away a great opportunity to win the title and can't believe what I've done," he said.
"I may never have another chance like this, being four frames ahead in a semi-final. After that first frame, you could see he was buzzing about the table.
"I expected him to come out and fight. He is probably the best player in the world."