A well-contested affair was decided by goals from Keyrol Figueroa in the first half and Tommy Pilling in the second.
Reds boss Rob Page made nine substitutions in the second period as he looked to keep his squad fit and sharp during a break in competitive fixtures.
The opening goal arrived on 15 minutes, after Salford failed to properly clear a corner.
Kaide Gordon picked the ball up on the right and went on a mazy run into the box that resulted in a goalmouth scramble, where Figueroa got the finishing touch.
Amara Nallo headed too close to the goalkeeper from a corner, while a fine run and cutback from the impressive Gordon led to Clae Ewing flashing a shot just wide as he arrived at the far side of the box.
Rhys Williams, Josh Davidson and Trent Kone-Doherty all arrived as half-time substitutes and Liverpool almost extended their lead just a few minutes after the break.
Figueroa jumped highest in the box and sent in an overhead kick that fell just the wrong side of the post.
However, Pilling made no mistake on 56 minutes, meeting a perfect cross from Kone-Doherty with a fine header, leaving the goalkeeper no chance.
Further changes followed for Liverpool, including Hadyn Murray-Holme stepping up from the U18s.
Oakley Cannonier also brought a fine save from the goalkeeper with an instinctive left-footed effort from a Davidson cross.
Liverpool U21s: Pecsi, Ramsay (Pitt, 75), Ewing (Davidson, 46), Nallo (Airoboma, 60), Trialist (R. Williams, 46), Kelly (Pinnington, 60), Pilling, Laffey (Murray-Holme, 70), Onanuga (Kone-Doherty, 46), Gordon (Morrison, 60), Figueroa (Cannonier, 70).
