Valley eased to their second big win at Butlin Road in three days, as they moved to the top of the UCL Premier table in the process.
Once Danico Johnson and the returning Ryan Seal had given the hosts a two goal lead with little more than a quarter of an hour on the clock, the hosts were in cruise control for large parts of the match that followed - with Seal grabbing a second after the break and Dylan Parker on target again at the death.
Johnson's sixth minute opener came after Charlie Evans had found the in-form striker and he beat two defenders with ease before curling his shot past Desborough keeper Chris Jones.
Town continued to press, and Jones was soon gathering a deflected effort from Liam Francis at the second attempt. Seal then successfully executed one of his trademark free-kicks from twenty five yards into the top corner to double the home side's advantage.
At the other end Jake Bettles should probably have done better when trying to slide onto a cross from Jack Wisniewski, whilst Parker nearly nipped in behind the visiting defence late in the opening period to almost take advantage of a loose ball.
Rugby started the second half strongly too, with a driving run and cross from Johnson just cut out by Aaron Davies. Cain Thomas blazed one over and Jones did well to block a Seal strike as the pressure intensified.
Jones's double tackle on first Seal then Evans just outside of his box kept his side in the game, but when Johnson's clever dummy to Caine Elliott's through pass released Seal through the middle once more, last season's top scorer made no mistake with a composed finish.
On his first appearance for the club from the bench the experienced Anthony Howell's attempted chip was caught by Jones, and Johnson then curled one just wide.
Parker's scissor-kick shot flew over and when Seal was again free on goal, he squandered the chance of a hat-trick by lifting the ball above the frame.
Wisniewski did twice go close for Desborough though - first shooting straight at Sam Lomax and then later the lofty stopper denied him with a good save with his legs.
Seal and Kurtis Revan both put in off-target efforts, before Parker made it four on the final whistle when he struck home Loyiso Recci's cut-back to the edge of the penalty area.
Line-up: Lomax; Recci, L Thomas, Clarke (C Thomas), Francis; Hancocks, Elliott (Howell); Parker, Evans (Revan), Seal; Johnson. Subs not used: Rosser. Booked: None.
Desborough line-up: Jones, Fowler, Bell, Morgan, Davies, D.Bettles, Wisniewski, Hayes, Gladman, Stevens, J.Bettles. Subs: Healey, Frietas, Cummins, Blaikie, Amos.