An own-goal from Rodney Brown early in the first half and a late clincher from the impressive Mark Randall secured the win for Tiernan Lynch, who will be hoping for another run in the Europa Conference League following their heroics last summer.
Larne made it through three rounds of the competition, and will now have to overcome the Glens at The Oval on Friday night to have any hope of repeating their exploits.
Experienced campaigner Jeff Hughes missed out completely for Larne with striker Lee Bonis replacing him in the starting eleven from the team which beat Crusaders in their final league game.
Oran Kearney made three changes to his Coleraine side which lost on the final day to Linfield. Ronan Wilson, Aaron Jarvis and Matthew Shevlin all dropped to the bench with Lyndon Kane, Matthew Shevlin and Eoin Bradley coming in.
Goalkeeper Gareth Deane missed a third game in succession with Marty Gallagher continuing to deputise.
Gallagher was forced into action on 12 minutes as he tipped a superb volley from Randall on to the bar and away for a corner.
The Bannsiders stopper though was left helpless from the set-piece as the hosts broke the deadlock in somewhat fortunate circumstances.
Kofi Balmer got on the end of Randall’s corner, his header was going well wide but it struck the unfortunate Brown and ended up in the net.
Randall was causing the visitors a lot of problems, and only a great block from Stephen O’Donnell prevented the former Arsenal man from adding a second.
Ten minutes before the break another Randall corner caused problems as it found Tomas Cosgrove at the back post, his header back across goal beat everyone but was hacked off the line by Kane.
The home side were well in control, but they couldn’t find the crucial second goal.
Former Coleraine man Ben Doherty was next to spurn an opportunity as he shot straight at Gallagher after being played in.
The second half continued in a similar vein with Larne creating chances. David McDaid fired straight at Gallagher on 52 minutes after Bonis had played him in.
Minutes later the Bannsiders carved out a good opportunity of their own as Patrick Kelly played in Jamie Glackin but his shot was held by Rohan Ferguson.
The Bannsiders were definitely posing more of a threat in the second period and the home support was starting to get a bit restless as we moved into the final quarter of the game.
And they should have dragged themselves level on 79 minutes as Bradley’s flick on found Steven Lowry, but his shot clipped off the foot of the post.
Six minutes of additional were added on at the end and the Bannsiders went close again as substitute Curtis Allen dinked an effort narrowly wide.
As the visitors pressed for an equaliser they were hit with a knockout blow as Larne scored the crucial second goal.
Andy Scott ran from his own half before teeing up Randall for a deserved goal and send his send into Friday night’s final.
Larne: Ferguson, Balmer, Kelly, Sule, Randall, McDaid (Scott 67), Doherty (Mitchell 85), Lynch (Jarvis 85), Bolger, Bonis, Cosgrove (c).
Subs: Devlin, Herron, Hale, Lusty
Coleraine: Gallagher, Kane, Mullan (Allen 86), Brown (Jarvis 53), Lowry, J McLaughlin (Shevlin 53), Bradley, Carson, O’Donnell (c), Glackin, Kelly (Wilson 78).
Subs: Henderson, K McLaughlin, Tosh.
Referee: Ross Dunlop