Three second half tries took Lancashire past their visitors to earn a seventh consecutive Twickenham final appearance next weekend.
A Jordan Dorrington score just before the break was added to by Ryan De La Harpe and Chris Briers before Dorrington completed a magnificent full-length run to score his second of the day to seal a fine win.
Yorkshire kicked off in the Lytham sunshine and immediately applied pressure to Lancashire's defensive line, pressure which paid off with a penalty try on 13 minutes with a penalty try given after a driving maul had been taken down.
Lancashire captain Evan Stewart was yellow-carded immediately, but his side kept Yorkshire at bay during his time out.
It wasn't long though until Lancashire were able to start applying pressure of their own, and it was Chris Johnson who had the first opportunity to score, but missed a penalty chance almost straight from kick-off. He rectified that on 20 minutes with a fantastic kick from virtually half-way to bring the scoreline to 3-7.
Both teams had men yellow-carded soon after, due to a handbag-slinging session, so Gareth Rawlings and Ali Thomson sat out the next ten minutes.
Johnson missed another penalty before going off for Steve Collins due to injury.
During a period in which the physics saw more action than anyone else, Anthony Bingham was another casualty after being taken out close to the touchline.
As half-time approaches, Jordan Dorrington put Lancashire into the lead for the first time, taking a pass from Scott Rawlings before racing 35 metres to score. Collins missed the conversion attempt from the right wing, for a half-time scoreline of 8-7.
Lancashire were able to open the game up in the second half, and De La Harpe found a gap under the posts to give Collins a simple conversion.
Yorkshire kept threatening, and were able to unlock Lancashire on the blindside soon after, but Joe Barker had gone into touch before putting down.
Dan Solomi's yellow card on the hour mark left Yorkshire exposed, and Briers scored after a Collins offload to make it 22-7 after the conversion, before the try of the game.
Dorrington, whose work-rate had been excellent all game, tackled in his own 22, and on collecting the ball, turned before slipping through the Yorkshire line and racing into Yorkshire's half. Stewart in good support, took his pass, and received the return to score between the posts for a quite remarkable try.
Collins converted for 29-7. Lewis Minikin breached Lancashire's line in the final minute for a consolation try which was converted by Joe Bedford, for a final scoreline of 29-14.
Lancashire's head coach Mark Nelson said afterwards: "It might have been a bit nip and tuck at half-time, but we came out and played some real quality rugby.
"At half-time we looked at discipline and clearing out rucks so that we had quality ball going forward.
"I don't think we played particularly poorly in the first half, just that certain things didn't stick at crucial times.
"There was more accuracy in the second half, we scored two spectacular tries, and what was good about today was that it was a 22-man effort.
"Everybody contributed significantly to the game today, and we're looking forward to another game against Cornwall in what should be a mother showpiece final."
Captain Evan Stewart spoke about the prospect of playing Cornwall in the final: "It's a team we know very well now, a third time playing them. It's another big challenge, a big step up, so training this week we will have to be spot on.
"The young lads should just enjoy Twickenham because the whole weekend goes in a flash, and hopefully we'll be coming back with the trophy."
"Being captain this season has been massive. Thinking about some of the players that have done it in my time with Lancashire, I've looked up to and revered, and having them still in the team has been awesome. You have Alex Loney, Chris Johnson and Louis McGowan, it's nice to have so many leaders in the team.
"It's been nice to have some young players coming through as well. I taught Jordan Dorrington when he was at Lancaster Royal Grammar School two or three years ago, and to give him the pass for his second try out there was very nice."
Lancashire team -
Warren Spragg, Jordan Dorrington, Chris Briers, Scott Rawlings, Anthony Bingham, Chris Johnson, Ryan De La Harpe; Ben Black, Alex Loney, Adam Lewis, Jonathan Nugent, Gareth Rawlings, Evan Stewart (Captain), Steve McGinnis, Matt Lamprey
Tries: Dorrington 38 71, De La Harpe 55, Briers 64
Conversions: Collins 55 64 71
Penalty: Johnson 20