Bas Savage stepped off the subs bench and picked the perfect time to score his first goal for Millwall with a 70th-minute strike to secure three crucial points at a wind-swept Huish Park.
Having stunned League One leaders Swansea City on Friday night, The Lions dug deep to clinch their second successive away win on the spin, and more importantly, open up a seven point gap on fourth from bottom Gillingham.
Savage, a 42nd-minute replacement for the injured Gary Alexander, applied the finishing touch to a slick Millwall move involving Lewis Grabban, Jay SImpson and fellow sub Ryan Smith.
It was Smith's introduction at the start of the second half and a switch to a more orthodox 4-4-2 formation that paid off handsomely for Kenny Jackett's side.
The Lions boss had stated before the match that he felt this fixture could be a a bit of a scrap, and the swirling, windy conditions did little to help the two teams produce much flowing football in the opening half especially.
Jackett stuck with the same starting line-up that produced a shock 2-1 success at Swansea, with the only change on the bench where Marcus Bignot replaced Zoom Bakayogo.
But whereas at the Liberty Stadium Millwall were ahead after 28 seconds, it could so easily have been Yeovil who drew first blood within the opening minute in this tussle.
Paul Robinson was penalised for a foul on Marcus Stewart and when Jaime Peters whipped in a freekick from the left, Zak Whitbread slipped enabling Scott Guyett a free header that caught the slightest of deflections for a corner.
When the ball was returned into the danger zone, Glovers debutant Jean-Francois Christophe's well placed header was held by Rhys Evans in the Millwall goal.
Keeper Evans came to the rescue again on seven minutes, this time superbly parrying Peters' stinging first-time shot for another corner.
After an indifferent start, The Lions began to settle and nearly scored with their first real attack of the half when a super move saw Grabban's 20-yard piledriver tipped over at full stretch by Scott Flinders in the home goal.
The game was played at a frenetic pace during the opening 20 minutes or so, but as a swirling wind became stronger, it was increasingly difficult to produce moves of real quality.
Andy Kirk's low effort on 21 minutes was parried low to Evans' right and then at the other end Jay Simpson's deep cross after 23 minutes seemed to hang in the air for an eternity before Guyett headed behind for a corner as the sides briefly exchanged chances.
A decent Lions move just past the half-hour mark involving Grabban and Danny Senda ended with the latter's delivery headed away for a corner, but there was little other first half action of note.
Jackett introduced Smith for Alan Dunne at the break and Millwall immediately enjoyed a spell of pressure, forcing three corners within seven minutes of the restart, with the outstanding Ali Fuseini a real driving force in midfield.
The Lions enjoyed the majority of possession, with Yeovil at times seemingly at a loss as to how to get the ball back.
However, it took until the 69th minute for Millwall to really get behind the home defence when Smith slipped a neat ball to Grabban, and his low delivery across the face of the home goal was hacked clear.
But within 60 seconds the deadlock was finally broken courtesy of Savage's clinical finish, although there was little opportunity for the big striker to show off his 'moonwalking' goal celebration at its best on a sticky Huish surface!
Smith went close to adding a second for the visitors with a superb bit of trickery and fierce 81st-minute 18-yard drive that flashed a foot wide.
Yeovil nearly grabbed a late equaliser, but Marc Laird was perfectly placed to clear Terry Skiverton's 90th-minute shot off the line and ensure that The Lions travelled back to SE16 with three more precious - and thoroughly deserved - points in the bag.

Yeovil Town: Flinders, Lynch, Skiverton, Guyett, Woods (Warne, 62mins), Barry (Owusu, 73mins), Stewart, Christophe, Peters (Williams, 22mins), Alcock, Kirk. Subs not used: Rose, Church.
Booking: Christophe (90+2mins)

Millwall: Evans, Senda, Frampton, Dunne (Smith, 46mins), Robinson, Whitbread, Laird, Fuseini, Alexander (Savage, 42mins), Grabban, Simpson. Subs not used: Edwards, Martin, Bignot.
Bookings: Dunne (43mins), Laird (82mins)
Scorer: Savage (70mins)

Ref: Rob Lewis
Att: 4,439