Terry Butcher's finished 11th in the Scottish top flight, ensuring that they would need to go through a play-off with Hamilton, second in the Scottish Championship, to make sure of their place in the division next season.
But the Edinburgh club produced a fine performance in Wednesday's opening game at New Douglas Park, Jason Cummings netting a brace to put the visitors in command.
The 18-year-old forward opened the scoring in the 39th minute as he capped off a Hibernian break with a fierce strike that flew beyond Hamilton goalkeeper Kevin Cuthbert.
And Cummings ensured that Hibernian will take a commanding advantage back to Easter Road when he struck a second in the 55th minute.
Cummings latched on to Paul Heffernan's delivery on the left-hand side of the box, with his shot crossing the line before Hamilton defender Ziggy Gordon could clear the ball away.
The result leaves Hamilton needing a substantial turnaround in Sunday's second leg to seal promotion.
