After falling behind to an early penalty Grangemouth struggled in the opening period.
Ward was given a yellow card for tackling a player after not retreating 10 metres at a tap penalty, but Dunfermline were unable to break down the home defence despite the extra man.
Skelton slotted a simple penalty to tie the scores as Stags, restored to 15, began to dominate and a Dunfermline prop was then given a straight red card for referee abuse.
In the second half Skelton made a half break before passing back inside to the supporting Gemmell for the opening try. Skelton was on target with the conversion but was wide with a penalty attempt a few minutes later.
Dunfermline levelled on the hour, driving through a lineout for a converted score but Stags were soon back in front.
For the second week in a row winger Allan weaved his way through several attempted tackles to run in under the posts, Skelton adding the extras.
In the closing stages the ball was moved wide for Gemmell to slide in at the corner for another try, but this time the conversion was wide.
In the final minute Stags collected the bonus point score when Dempsey fired a long pass to Gemmell to run in at the corner to complete his hat-trick. Skelton added the conversion to make the final score 29-10.
This week the Stags are again at home as league leaders Caithness make the long trip south. Kick-off is 3pm.
The 2nds lost 26-25 to Angus Development XV at Montrose to take on Angus Development XV despite outscoring their opponents by five tries to four. Try scorers were Hendry (3), Michie and Hunter. This week the 2nds are also at home against Waid with KO 3pm.
Grangemouth Ladies played Aberdeenshire Ladies on Sunday with the Stagettes winning 27-22. This Sunday the ladies are back in cup action at home to Melrose at 2pm