Prior to the opener, the Inver Reds had squandered two gilt-edged opportunities. Bolger's glancing header from Mark Randall's corner flashed across goal, with Jordan McEneff agonizingly close to connecting.
Four minutes later, Benji Magee inexplicably missed from six yards after Andy Ryan's deft header set up the former Loughgall man.
After the break the away side came within inches of doubling their lead. Ryan's curling free-kick in the 56th minute beat McCarey but crashed against the upright. This near-miss seemed to galvanize the hosts, who began to assert themselves.
The Mid-Ulster side's persistence paid off in the 64th minute when Fyfe drew them level. Mark Randall's careless turnover allowed McCartan to find Paul McElroy, whose inswinging cross was met powerfully by Fyfe as he headed in.
As the match entered its final stages, both teams pressed for a winner. Larne's Paul O'Neill forced McCarey into a diving save from a free-kick, while at the other end, Fyfe was denied by Rohan Ferguson when through on goal.
However, the defining moment arrived in the 88th minute courtesy of an extraordinary strike from McCartan. The Portadown man, spotting Ferguson off his line, launched an audacious lob from inside his own half that sailed over the stranded keeper, sending Shamrock Park into raptures.
Larne must quickly regroup as they seek to defend their title, while the hosts will look to build on this morale-boosting triumph in the coming weeks.