However the Drogs hit back through Graham Gartland ten minutes after the break, making it 2-2 on aggregate, with both sides holding onto an away goal.
The score stayed level until full-time but Lynch scored from the penalty spot on 97 minutes to put his side in front. Helsinki's Aho was sent-off two minutes later to give the home side added incentive.
Lynch put the icing on the cake minutes from the final whistle as he blasted his spot-kick straight down the middle after Shane Barrett had been brought down in the penalty area.