Celtic battled through to the next preliminary round of the FA Cup with a goal in each half and now face North Ferriby in the next round.
They grabbed the opener when Chasetown failed to clear a free kick and Aaron Chalmers drove a ball through a crowded box Jack Higgins had the presence of mind to stick out a foot and drove the ball into the bottom corner.
After the second half, Chasetown started to slow down, but on the hour a snap shot from the edge of the box had to be pushed round the post at full stretch by Tony McMillan.
Then Chasetowmn's Danny Edwards thought he’d beaten the offside trap when he latched onto Michael Williams’s long diagonal ball, and fed it into the path of Ryan Winter to slot home but celebrations were cut short with the offside flag up for Edwards, leaving Winter on his knees in frustration.
As stoppage time approached Celtic's Osei showed great composure instead of taking a shot himself, he squared it to Adam Farrell who arrived at speed at the back post, he the simplest of finishes to give Celtic the safety net going into stoppage time.