The midfielder's cross cum shot beat Forest Green keeper Steve Williams all ends up to settle a hard-fought contest on the South Coast.
The goal ensured Garry Hill's men got back to winning ways after two draws and a defeat, extending a run of only one home League defeat since March 2004.
Defeat was probably harsh on Rovers who battled well under new boss Jim Harvey and will surely pull away from the foot of the table with more performances like this over the coming weeks.
Weymouth took a long time to get going though and it was Harvey's bottom-of-the-table side who had the better of the early exchanges.
With winger Les Afful lively for the Gloucestershire visitors it was the former Exeter City youngster who created the best of the few openings that did arrive before the break.
Afful linked up well with lone striker Alan Russell, cut in from the right, and squared for Alex Meechan only for Terras keeper Aaron Lee-Barrett to block at the near post.
Weymouth were struggling to get going as the hosts continually launched high balls for frustrated strikers Raphael Nade and Richard Logan.
Having lost striker Chukki Eribenne to a nasty head injury at Burton last Saturday, the hosts suffered another major blow midway through the opening half.
Defender Ashley Vickers was stretchered off with a leg injury after he was caught trying to block Russell's long-range shot.
Meechan then tried his luck from distance for Rovers but his shot was easily saved by Lee-Barrett.
As the interval approached Weymouth improved and could easily have gone into the break ahead.
Lone striker Nade sent a snap shot just wide, then Tony James and Nade combined to find Ben Smith.
But as the midfielder ran into the area, the ex-Hereford United star was bundled out of possession by the quick-thinking Afful.
Weymouth's best two chances of the opening half came in the closing seconds of the half.
Lee Elam's well-flighted cross was headed down by Logan for Crittenden who drew an excellent double save from Williams.
Moments later Smith floated over a cross for Nade but the striker headed wide from six yards.
Forest Green nearly hit the front within seconds of the restart when Afful sent in an angled shot which clipped Lee-Barrett's left-hand post.
But slowly and surely Weymouth began to take a stranglehold as Smith flashed a shot over and Crittenden followed from range moments later.
By now a Weymouth opener seemed inevitable and it duly arrived on the hour following a mistake by Rovers' defender Darren Jones who gifted the hosts a corner.
Elam took the resulting kick down the left, short to team-mate Crittenden, he swung over a superb cross, which confused keeper Williams all ends up.
Weymouth's Smith was lurking close by but the ball sailed straight into Williams' top corner.
Logan nearly doubled Weymouth's lead with a thunderbolt of a free-kick and a Smith angled drive also was not that far away.
Rovers boss Harvey replaced the lively Afful with substitute Charlie Griffin on 70 minutes and the move nearly paid off instantly.
Jamie Pitman swung over a free-kick from the left flank and striker Griffin stole a march on his marker, only to see his header flash inches past Lee-Barrett's post.
Weymouth boss Hill countered by withdrawing striker Logan for substitute Jason Tindall who performed as a defensive midfielder.
Elam nearly sealed the points for the Terras with a low shot, but there was nearly late drama at the other end.
Meechan crossed for Russell in a good position but the striker's goalbound flick was gratefully grabbed by keeper Lee-Barrett.