Alloa clinched a top-four finish as Kevin Cawley's second-half goal secured a tense 1-0 win over fourth-placed Forfar.
Paul Hartley's men are now 15 points clear of fifth placed Arbroath, who lost to Brechin, and will take part in the play-offs.
Cawley was denied a 25th-minute opener as his shot from the edge of the area was tipped over the crossbar by visiting goalkeeper Darren Hill.
Hill's counterpart Scott Bain was also in top form at the other end, diving down well to push away Danny Denholm's close-range effort just before half-time.
The only goal came two minutes after the break as Ben Gordon found Cawley in the area and the striker tucked in his 11th goal of the season.
Substitute Martin Grehan headed over from close range as Alloa looked to kill the game off, but the miss proved not to be costly as Forfar were unable to find a leveller.