The performance saw the hosts secure consecutive wins of that margin and their fourth league triumph in a row.
Ryan Seager was typically composed in handing Southampton an early lead that Sam McQueen built on with an easy finish from similar range.
Fulham threatened to halve the deficit shortly after the break but Dino Islamovic’s penalty rattled the woodwork and rolled away to safety.
Sam Gallagher completed the victory with a rebounding effort from point-blank distance as third-placed Saints strengthened their assault on the top of the Barclays Under-21 Premier League table.
In identical fashion to the manner in which Saints Under-18s weren’t fazed by then-league leaders Fulham last Saturday, Martin Hunter’s side began the encounter against the Cottagers’ U21s in desired fashion with a fourth-minute opener.
SEAGER repaid the coach’s faith in starting him by driving into the box and calmly side-footing across onrushing ‘keeper Jesse Joronen and into the far carner.
The forward’s opener proved to be the catalyst for a dominant period from Saints which consisted of a glorious opportunity wasted by Gallagher two minutes later when he rose to nod Jake Sinclair’s cross well over.
A thoroughly encouraging first half for the hosts was interspersed by the occasional chance for Fulham, Alex Brister’s drive narrowly over the crossbar on the quarter-hour mark being one of two dangerous attempts from the Cottagers.
That was followed by some heroics from Joronen, whose double save kept Saints at bay after his stop from Seager preceded a parry to prevent McQueen’s deflected, looping follow-up.
Ange Freddy-Plumain rapidly ghosted past a challenge before whipping a 25-yard shot that dipped marginally wide before MCQUEEN found the net at the second time of asking with three minutes remaining in the opening half.
Gallagher took a pass into his stride in the area and laid it across for McQueen to tap the ball into a gaping net from close-range.
McQueen returned the favour to his fellow forward on the stroke of half-time with a cross to Gallagher but he failed to draw the same result as he side-footed a volley back across the face of goal and wide.
HALF-TIME: SOUTHAMPTON U21s 2-0 FULHAM U21s
Saints certainly didn’t continue in the same way immediately after the restart when they conceded a penalty through Turnbull being judged to have brought down Joshua Pritchard in the box, despite the defender’s protests that there was no wrong-doing.
Islamovic assumed the spot-kick duties and failed to convert as his side-footed attempt was hit too wide and rattled off the outside of the post.
McQueen spurned an opportunity to seal a brace when he broke through Fulham’s backline as he preferred power over precision, drilling the ball straight at Joronen.
By the 53rd minute, all of Saints’ three-pronged attack had found the net when GALLAGHER’s rebounding effort put the game beyond the visitors.
Joronen failed to hold Sinclair’s stinging effort and saw it ricochet off him and roll into the path of Gallagher for a tap-in from inside the six-yard box.
Fulham’s afternoon didn’t improve with just over 20 minutes remaining when a rare glimpse of goal from close still reaped no reward.
The ball was pulled back to Pritchard who scuffed a tame effort from the centre of the box that Gazzaniga smothered with ease.
Omar Rowe, who replaced goalscorer McQueen, made a positive impact from the bench yet again when his burst down the wing created space for him to fire a cross in that Fulham were fortunate to see scoped just over the goalframe by the retreating Charles Banya’s slide.
Fortune continued to elude Pritchard whose 25-yard shot soared inches over the crossbar as Southampton sealed consecutive three-nil wins.
FULL-TIME: SOUTHAMPTON U21s 3-0 FULHAM U21s
Southampton Under-21s: Paulo Gazzaniga, Jason McCarthy, Matt Targett, Dominic Gape, Calum Chambers, Jordan Turnbull (c), Jake Sinclair, Harrison Reed (Jake Flannigan 82), Sam Gallagher, Ryan Seager (Jake Hesketh 87), Sam McQueen (Omar Rowe 69). Unused substitutes: Josh Debayo, Cody Cropper.
Fulham Under-21s: Jesse Joronen, Alex Brister, Matthew Briggs (Aaron Redford 45), Joshua Pritchard, Mananga Jonathan Buata, Joshua Passley, Ange-Freddy Plumain, Lasse Vigen Christensen, Dino Islamovic, Chris David (Joshua Smile 45), Lyle Della Verde. Unused substitutes: Max Oberschmidt, Joshua Smile, Daniel O’Reilly.