Westbury are completely locked into a three-way title race with just one point separating them, Roman Glass and Keynsham.
United overcame a slow start to turn on the style in what was a brilliant performance against a Welton side who had won 6-2 a few days earlier.
Rovers started brightly and Lewis Porter did well to turn away Charles Courtnay’s shot.
Westbury gradually got going with Jake Hiscocks, Josh Ferguson, Joe Stradling and Jamie Jordan all prominent from midfield, while Mark Robinson and Dan Kovacs looked in continued fine form up front.
Visiting keeper Tom Drewitt saved twice from Kovacs before a great move between Robinson and Kovacs sent the latter through one-on-one, only for Kovacs to miss the target.
There was bemusement when Joe Garland only received a yellow card after flattening Kovacs.
Still, Westbury kept playing fast-paced football and the opening goal came on 37 when Stradling sent in a fine cross, which was headed powerfully past Drewitt by Ferguson.
United were flowing forward and Robinson hit an audacious attempt which was spilt wide by Drewitt; from Jordan’s corner Matt Jones half volleyed inches over. The same combination happened again just after with Jones again narrowly missing.
Kovacs thought he had made it 2-0 on 42 but he was flagged offside. However there was no doubt 3 minutes later when he finished with ease to double the lead going into half time.
The hosts continued attacking after the break. Dan Price headed wide from another Jordan corner, then Drewitt did well to parry Robinson’s well-struck volley. The next chance saw Kovacs and Stradling combine to tee up Jordan, but his effort was blocked inside the 6 yard box.
A third goal seemed imminent and it came fortuitously/amusingly depending on your viewpoint as confusion between Drewitt and Tom Smith caused Smith to panic and lob the ball skywards where it then dropped and bounced over the line!
Kovacs quickly made it 4-0 on 69 with a classy finish after more great play by Robinson and Jordan.
Rovers had their best spell of the game around the 75th minute with a sustained spell of pressure seeing chances for Malick Jammeh, Courtenay and Aaron Cornwall, all blocked by the strong home defence.
Stradling was denied a goal by a brilliant goal-line clearance by Smith, then Welton grabbed their consolation goal from the penalty spot when Steve Hulbert brought down Jammeh who got to his feet and scored the kick.
STAR MAN ; unable to single any player out. TEAM ; Lewis Porter, Steve Hulbert, Leon Greenland, Jake Hiscocks, Dan Price, Matt Jones, Jamie Jordan, Josh Ferguson, Mark Robinson, Dan Kovacs, Joe Stradling. SUBS ; Jordan Pinder, Ricky Hulbert, Martin Johnson (used) Joe Kirkpatrick, Dan Jordan (unused)
Andy Bown