Darryl Meggatt's first goal for Alloa helped inflict a 1-0 defeat on promotion-chasing Hamilton.
The Accies went into the game three points clear at the top of the table but were replaced by Dundee after suffering their second consecutive defeat.
Louis Longridge went close to an early opener but fired just over Scott Bain's crossbar after five minutes.
Anthony Andreu had a good chance for the visitors 10 minutes before the break, but smashed from over the bar from inside the area.
But Alloa were quick out of the blocks in the second-half and took the lead as Ryan McCord's cross to the back post found an unmarked Meggat who nodded in.
Andrew Ryan was denied an equaliser by a stunning save from Scott Bain, who pushed away the substitute's fierce drive from the edge of the area.