Leeds fell behind in the 20th minute as keeper Dani van den Heuvel failed with his attempts to punch clear a corner which landed at the feet of Irons captain Kaelan Casey whose first time attempt was judged to have crossed the line despite Kris Moore's attempts to clear.
But a series of van den Heuvel saves then helped Leeds stay within one goal of a dominant Hammers, ultimately paving the way for the Whites to equalise two minutes before the break. The nifty Sean McGurk released Connor Douglas down the left flank and Douglas then beat two men as he cut into the area before smashing home a strong drive into the bottom right corner.
Leeds had earlier gone close through Luca Thomas whose fierce strike from inside the box was tipped over the bar but West Ham went back in front in the 46th minute after excellent striker play from 18-year-old Northern Ireland senior international Callum Marshall.
A series of passes saw the Irons pick their way through the Whites midfield and work the ball to Marshall who turned Moore on the edge of the box before firing a shot through his legs into the opposite right hand corner of the goal.
Marshall, already capped for Northern Ireland, had been a constant threat and the teen then bagged West Ham's third goal and his second just four minutes after the interval through a lovely flicked finish to a cross from Gideon Kodua who had been played in down the left flank.
Marshall then squandered a fine chance to complete a hat-trick when sending close-range header over the bar at the far right post. Leeds attempted to respond for a second time and Thomas narrowly failed to connect to a Ferguson cross which flew through the box.
But West Ham were continually causing problems to United's back line and the Irons added a fourth goal in the 68th minute through Ollie Scarles who was afforded far too much space in the box and took advantage with a bullet finish into the far right corner.
Leeds continued in their attempts to pull a goal back but another Irons attacking menace in George Earthy squandered another glorious Hammers chance when skewing his shot wide after being played in behind the Whites back line.
But the Irons weren't done and there was still time for Marshall to complete his hat-trick with a composed finish after a neat through ball from Earthy had played him in on goal.
Even then the scoring was not done and Leeds pulled back a late consolation through a fabulous goal from substitute Cian Coleman who received the ball in the middle of the park before storming forward and unleashing a powerful drive which had too much venom for keeper Knightbridge to keep out.
Leeds United under-21s v West Ham under-21s: Van den Heuvel, Ferguson (Godden 83), Moore, Monteiro, Mullen (Debayo 56), Jenkins (Spencer 56), Crew, Douglas, McGurk, Carole (Coleman 70), Thomas. Subs not used: Ombang.