A goal in each half from Darren Barr and Graham Barrett settled it but Falkirk could have won by much more as they dominated the second half.
The Bairns created a chance after a couple of minutes when the inventive Russell Latapy picked out Carl Finnigan with a short free-kick into the area, but the striker looked as surprised as the Gretna defence as he failed to make clean contact.
However, Gretna responded and it took a last-ditch tackle from Barr to keep out Fabian Yantorno after a clever head-flick from James Grady.
Grady then tested Tim Krul with a header after Evan Horwood and Erik Paartalu had combined to give him the chance.
Pedro Moutinho tested Greg Feming with an angled shot which the goalkeeper dealt with comfortably.
Patrick Cregg came closer midway through the first half when the ball broke to him at the edge of the box but his right-foot shot was just a yard wide with Fleming struggling to cover his post.
Moutinho should have done much better when Latapy found him in splendid isolation in the Gretna penalty area but he lacked composure and thrashed his shot wide.
Falkirk stepped it up towards half-time and Finnigan played in Cregg but he was crowded out before he could pull the trigger.
John Hughes' side had what looked like a certain penalty waved away by referee Craig Thomson when Fleming pulled back Barrett and, in the confusion that followed, the ball looked to strike Danny Grainger's hand. Gretna were hanging on the ropes by this stage.
Fleming made an excellent reaction save to keep out a right-foot shot from Barrett at his left-hand post but the opening goal finally came four minutes before the break and it was simplicity itself.
Gerard Aafjes picked out Barr with a deep cross and the skipper was unmarked as he headed the ball beyond Fleming.
Any hopes Gretna had of salvaging the match were effectively over five minutes into the second half when they failed to deal with a long throughball from Aafjes and Barrett nipped in to provide an assured finish.
Barrett should have made it 3-0 when Moutinho set him up but he pulled his 15-yard shot wide.
Gretna had another let-off when Horwood looked to handle the ball in the area when Latapy touched it past him but again the referee was not interested.