The home team were made to work hard for the victory, especially in the first half when only some fine saves by keeper Artur Boruc denied the visitors.
As it was, Scott McDonald put Celtic ahead ten minutes from the interval and when Scott Brown made it two for the home team just after the restart, Celtic were in control.
Celtic had to wait until the final minute before Aiden McGeady shot home their third with the aid of a deflection off the unfortunate Ryan McGuffie.
It was Gretna who threatened early in the match with Boruc saving well at the feet of Nicky Deverdics.
Gavin Skelton shot wide from 20 yards before the visitors nearly opened the scoring.
Evan Horwood's free-kick from the halfway line was volleyed by Allan Jenkins from six yards, but Boruc somehow managed to parry his effort.
Celtic were struggling to assert themselves against the bottom team in the league and Fabian Yantomo's powerful shot on the turn from ten yards was blocked by Boruc with Kenny Deuchar hitting over the rebound.
Celtic took the lead in almost their first attack of the half. Boruc's long clearance was headed on by Jan Vennegoor of Hesselink to McGeady, who passed to McDonald to shoot home from 18 yards off the inside of the post.
There was still time for Boruc to produce another fine save to deny Yantomo with Lee Naylor completing the clearance.
Gretna would have been encouraged by their first-half display but fell further behind soon after the restart.
McGeady and Gary Caldwell combined well on the right before releasing Brown, who shot low into the corner of the net from 18 yards.
The visitors nearly reduced the leeway when Horwood's free-kick was punched against Deuchar by Boruc, but as the ball rolled towards goal, Caldwell cleared off the line.
Only the woodwork prevented Celtic adding to their lead as Paul Hartley headed against the bar, before McDonald was equally unlucky when his shot on the turn came back off the post.
Celtic made their victory more emphatic with a goal near the end.
McGeady cut in from the left and his powerful shot from 20 yards beat keeper Tony Caig thanks to his slight deflection off McGuffie.