An Andy Ryan finish in the closing moments was enough to secure Larne's place in the last four of the Samuel Gelston's Whiskey Irish Cup at the expense of H&W Welders.
The Premiership leaders were made to work all the way by their Championship hosts in an intriguing, hard fought encounter at the Blanchflower Stadium.
The game got off to an energetic start with the first attempt on goal coming early on for the hosts when Matthew Ferguson forced keeper Rohan Ferguson to backtrack to deal with his goalbound header moments before Michael McLellan almost made the most of a defensive error but could only fire across the face of goal.
But, as the visitors settled into the game, they began to assert their dominance and might have edged into the lead had Paul O'Neill's free header not been dealt with by defender James McCarthy.
Kyle Owens then showed his experience to block an Andy Ryan effort before keeper Michael Argyrides - named the Championship Player of the Month for February - pulled off an incredible save followed by a Ferguson goalline clearance.
Larne's next effort came through Daniel Kearns from around 20 yards only for Argyrides punched clear while, at the other end, Jonny Frazer sent a right-footed shot just past the far post.
The Welders came storming out of the blocks after the break, coming close through Ferguson's effort over the top followed swiftly by a Joe Thomson clearance off the line to thwart Owens.
The visitors threatened via Shea Gordon at the near post but, again, Argyrides did well to get down low. Thomson was next to test the home keeper after twisting and turning in the box albeit, once more, without a positive outcome.
However, just seconds towards the end of the 90 minute mark Larne substitute Lee Bonis teed Scotsman Ryan up with a through ball to nip in and direct what proved to be the winner past the Canadian keeper to break the Welders' hearts much to the relief of the sizeable visiting support.
HW Welders: Argyrides, Patterson, McCarthy, Byers, Owens, Kinner, Frazer, Harris, Ferguson, McLellan, Farren Subs: Lanouette, Akassou, Wilson, Garrett, McMurray, Galbraith, McGuiggan
Larne: Ferguson, Want, Watson, Kearns, O'Neill, Donnelly, Gordon, Thomson, Glynn, Cosgrove, Ryan Subs: Pardington, Sule, Bonis, Hutchison, Maguire, Banda, Aretzis