Mark Percival's second attempt at Leeds was enough to end any hopes of a Leeds comeback.
Betfred Super League semi-final St Helens (14 Tries): Grace 2, Roby 2, Percival 2, Naiqama Goals: Coote Six Leeds (4) 8 Tries
After beating Leeds Rhinos, St Helens booked a Super League Grand Final with Catalans Dragons.
Regan Grace gave the reigning champions a lead early on, which James Roby extended just before Richie Myler put Leeds on the board.
Saints extended their lead to 24-4.
Leeds had hope when Luke Briscoe came through, but Percival Grace and Grace crossed again to ensure Saints' participation in the third Grand Final.
St Helens won the showpiece last season by beating Wigan in Hull. Now, they will return to Old Trafford, the site of their Grand Final victory against Salford in 2019, to face the League Leaders Shield winners a week later.
Saints, the Challenge Cup winners, showed no signs of slowing down in their quest for silverware. Kristian Woolf's team showed their dominant steel to keep their hopes alive of a three-peat'.
Saints beat Leeds in a frenetic atmosphere as many players said goodbye to home. They scored a fast first quarter in each half to win the game.
As he did in their regular season meeting a few weeks ago, Alex Walmsley caused havoc with his powerful carries. Jonny Lomax and Lewis Dodd, who each kicked six goals, were able to open the doors for the visitors.
Percival and Grace were both able to finish the game twice after making sharp left-hand moves. Roby's sniping efforts and Naiqama’s farewell score in the final home game before he returned to Australia for family reasons at end of season were equally well received.
Leeds displayed character by staying in the game even when Saints seemed to have it won. Their reward was Myler's clever cut back inside and Briscoe finishing in the corner under Dodd's pressure.
One disappointing aspect was the high number of yellow cards. Four players spent 10 minutes in the sinbin. Morgan Knowles might have had to wait nervously for the judiciary to determine if he would be available next week's final following his late shot on Kruise Leming.
Richard Agar and Richard Agar's Rhinos bid farewells. Rob Lui, Konrad Hurrell, and Konrad Hurrell left after the game. However, it was Saints night after a dominating display.
Kristian Woolf, St Helens coach, spoke to BBC Radio Merseyside
"I thought that right from the beginning, we displayed a great intensity. We held that intensity throughout the entire game.
"We haven't won anything yet. There is still much to do and a lot of work ahead.
"We are facing a very, very difficult side in Catalans.
"One thing that I know is going to happen in this group is that they will give everything they have.
Leeds Rhinos coach Richard Agar told BBC Radio Leeds:
"[We] were beaten by a stronger team on the evening. We failed to execute and reach the goals we wanted to achieve.
"Some of this [blame] should go to us, but also the constant pressure they placed on us and the speed with which they used their power.
"They set the tone defensively well and made it difficult for us.
"Our start wasn't where we wanted it to be, but we showed plenty of fight,"
St Helens: Coote; Makinson, Naiqama, Percival, Grace; Lomax, Dodd; Walmsley, Roby, Lees, Mata'utia, Batchelor, Knowles
Interchanges: McCarthy-Scarsbrook, Amor, Paasi, Welsby
Sin-bin: Mata'utia (29), Knowles (66)
Leeds: Myler; L Briscoe, Newman, Newman, T. Briscoe, Handley; Lui, Leeming; Oledzki, Dwyer, Prior, Donaldson, Martin, Tetevano
Interchanges: Smith, Holroyd and Thompson
Sin-bin: T Briscoe (20), Donaldson (44)
Referee: Chris Kendall
