In a low-key opening half, Coleraine almost scored after just five minutes when Matthew Shevlin burst clear of Sam Todd on the halfway line and raced towards goal.
With little in the way of support Shevlin opted to shoot himself, forcing Larne ‘keeper Rohan Ferguson into a smart save at his near post.
Larne had a penalty appeal for handball turned down by referee Ben McMaster midway through the opening half and shortly after had a second appeal waved away when Sean Graham went down under a Jamie Glackin challenge in the box.
The action picked up quickly after the break as the hosts opened the scoring with O'Neill, recalled in the absence of leading scorer Andy Ryan, nipping in front of his marker to guide Joshua Seary's cross home from close range.
Larne's lead lasted only 10 minutes, however, as Glackin hit back for Dean Shiels' side. Coleraine captain Lyndon Kane made great ground down the right wing before unselfishly squaring for the midfielder to sweep home from 12 yards.
But Larne regained the lead after 63 minutes as former Coleraine player McKendry's powerful drive shot from 30 yards escaped the grasp of Bannsiders keeper Max Little before ending up in the back of the net.
The hosts, however, had defender Logan Wallace - who turned 19 on Sunday - to thank for preserving their lead with virtually the last action of the game after he poked the ball behind for a corner with Shevlin poised to tap home.