A late effort from captain Holly Reid and a catastrophic goalkeeping error from Mackenzie Ellingham were enough to move Exeter within four points of the hosts in the table.
Going into the clash, the hosts were just two points behind Bristol at the summit of the table, albeit having played a game less.
However, despite a resilient 3-2 victory over Cardiff Met last time out, USW flattered to deceive in a lacklustre display undermined by individual errors.
A defensive lapse in concentration put Sammy Kirk through on goal early on, and she dispatched neatly to score – only for the offside flag to dampen the celebrations for the visitors.
The indoor setting did very little to stifle the bitter cold, which took a while for both sides to acclimatise to.
Home captain Tate Trivett went close as USW built some momentum, and Caitlin Seaborne glanced a header downwards from close-range, only for her effort to be kept out by Sophie Mitchell.
Pic: Ed Bregua
Exeter were content to concede the possession game, but counter-attacked with voracity.
However, their end-product let them down – efforts from Noemie Pacette and Zoe Anderson were flashed over early in the second-half.
The turning point came when some fancy footwork by Poppy Kelly saw her round the goalkeeper and eventually find Reid in space inside the 18-yard box, whose shot trickled around the defence and went in.
Then, USW’s Maddie Williams received a sin-bin following dissent, prompting an animated debate between the fourth official and hosts’ coach Kathryn Morgan.
Ellingham almost got caught out when a simple distribution was intercepted and tapped in, but the officials once again bailed out the home team with an offside decision.
But there was no respite when a headed effort bounced off the palms of USW’s goalkeeper and ricocheted into the net, much to the embarrassment of the home side.
Ultimately for USW, it was a similar story to their October loss to Bristol, with plenty of guile but a lack of clinical edge –Exeter’s euphoric celebrations at the end of the game indicated the significance of their win.
USW must now must respond when they welcome Hartpury to Trefforest next Wednesday.