Robbie Conway and Roan Turkington each scored doubles, which were complemented by single strikes from Ross King and Aidan Holligan to send Cavalry through with little fuss.
The Capital youngsters were far too strong and well-drilled for their west counterparts, dominating for long periods and raining the shots towards visiting goalkeeper Craig Melrose.
George King and his Cavalry coaching team willed their team through the game with constructive encouragement, while Erskine's young players appeared increasingly nervous amid decidedly negative calls from their own management.
A large and often-vocal crowd gathered for the game and, coupled with the teeming rain and mudbath of a pitch, created a real cup-tie atmosphere in which the Cavalry youngsters revelled. The hosts' diminutive front pairing of King and Conway was particularly impressive, and the latter opened the scoring after just five minutes.
Seven minutes later, Nathanial Harvey squared for Turkington to sidefoot home from close range as Cavalry grew in confidence, extending their lead.
Conway then screwed his shot wide at a one-on-one with Melrose, and shortly after was thwarted in a similar situation by the goalkeeper, who smothered at the striker's feet.
Erskine pulled a goal back on 25 minutes after Thomas Kerr's surging run down the left, the tallest player on the park reaching the edge of the box before playing in team-mate Adam Glen, who struck past Calum Eastwood from 12 yards out.
A delightful goal shortly before half time restored Cavalry's two-goal advantage, though, as King and Conway combined superb precision and timing to tear apart Erskine's defence. Conway picked up the ball on the halfway line with just his fellow striker for an ally, running the ball forward in the face of three Erskine defenders before releasing King on the right. Conway then stormed into the penalty area while King continued the flow forward, and was perfectly placed to regain the ball from an inch-perfect King pass, stroking the ball into the net from six yards.
Erskine fought back again immediately after half-time, Glen grabbing his second to reduce the deficit to 3-2, but from there it was the home side who masterfully strolled through the game, adding goals four, five and six.
Holligan's tantalising cross from the right was, agonisingly, just a long toe-nail away from the end of Conway's right boot, but seconds later a great Adam Watson cross from the opposite flank was controlled and converted by the composed King.
King was denied by Melrose five minutes later, and the impressive goalkeeper pulled off an outstanding full-stretch save to tip away Watson's effort after the striker had charged down a goalkick. Unfortunately for the No.?1, his save was in vain as the ball fell invitingly to the far post where Cavalry's King and Holligan lurked, and the latter stabbed the ball into the net.
Watson provided a third second-half assist with eight minutes of the match remaining, whipping in a corner from the right for defender Turkington to net his second of the game from point-blank range.
George King, the Cavalry Park coach, was understandably pleased to see his side win with such style.
He said: "We've been doing okay this season. We knock the ball about well, and the coaches here are trying to teach the boys to play properly. We've won most of our games this season by playing football, but it's not all about winning."
Cavalry Park: Calum Eastwood, Ben Stirling, Roan Turkington, Cal Sheridan, Stephane Murray, Jackson Barker, Sam Nicol, Aidan Holligan, Adam Watson, Jack Kidney, Ross King, Robbie Conway, Sean Gilroy, Nathanial Harvey.
Erskine YFC: Craig Melrose, Iain Corbett, Thomas Kerr, Andrew Brodie, Thomas Kerr, Argyll McCoist, Thomas Stewart, Callum McMurchy, Myer McKinnon, Adam Glen, Jordan McDonald, Aarron Christie, Nathan Lang, Ryan Quinn, Kyle Edgar, Aidan Wilson.