Archibald Campbell and Kyle Wilkie were on target as Morton beat Livingston 2-0.
But Morton face another season in the First Division after Partick sealed the title with a 2-0 win over Falkirk.
The hosts started brightly and had a number of chances to take an early lead but none of their efforts from range troubled Morton stopper David Hutton.
The tables turned in the closing stages of the first half and the visitors began to push for the opening goal.
Wilkie hit the post from 30 yards out before they finally broke the deadlock moments later.
Campbell latched onto Colin McMenamin's pass before tapping the ball past Darren Jamieson from close range.
Wilkie made it 2-0 10 minutes after the restart when he slotted the ball into the bottom corner six yards out.