Neither side produced much in the way of quality in a scrappy, wind-affected affair that saw the O's slip back into the relegation zone.
In a game that never lived up to its relegation six-pointer hype, it was the Glovers who went closest early on with first Shaun MacDonald forcing a save from Jamie Jones after good work on the left and then Craig Alcock firing wide from 20 yards after dispossessing Dean Morgan.
The home side looked the better in possession as the Glovers went close again on 20 minutes with Aaron Brown heading straight at Jones from an Andy Welsh free-kick.
Meanwhile, the O's had to wait until first-half stoppage time to come close when Morgan fizzed a free-kick narrowly over the bar from an acute angle.
The quality of football deteriorated further after the restart as neither side managed to cope with the windy conditions.
O's defender Tamika Mkandawire did well to put behind a dangerous cross from Nathan Smith on 51 minutes and a minute later striker Ryan Jarvis came closest for the home side, volleying over from 20 yards after a move of rare quality.
Both goalkeepers continued to be spectators for the majority of a stop-start second period with set plays creating the only real half chances for either side.
And it was a set play that won it when Tomlin leapt to head home Welsh's corner in the fifth minute of stoppage time to snatch victory in a game that neither side deserved to win.