The Blues second string were impressive in the first half an hour of the game - Ricardo in the United goal forced to pull off numerous saves to deny Blues the lead.
Craig Fagan and the dangerous Jovan Kirovski went closest but the Spanish stopper kept them out.
However, midway through the first half it was United who finally managed to find the breakthrough - Forlan scoring after good work from Nardiello, who played the ball across the face of goal for the Argentine to tap home.
On 51 minutes Nardiello doubled the home sides lead, beating two Blues defenders before shooting past Bennett to make it 2-0 to the Reds.
And to complete a poor night for Blues, Nardiello scored his second goal and United's third from the penalty spot in the 72nd minute after he had been bundled over in the box by Blues defender Curtis Woodhouse.
Blues: Bennett, Beauchamp, Hutchinson, Tebily, Woodhouse, Grondin, Hughes, Carter, Kirovski, Fagan, Evans. Subs: Parker, Allen, Barrowman, Davies, Capaldi.
United: Ricardo; Lynch, Tate, May, Rankin; Chadwick, Pugh, Richardson, Fortune; Nardiello, Forlan. Subs: Roche, B Williams, Fox, Timm, Johnson.