The young Reds went behind 66 minutes in at the Joie Stadium, when Divin Mubama’s header found the bottom right corner.
United pushed for an equaliser in an even and fast-paced game, but couldn’t overturn the one-goal deficit. Instead, Mubama's clever 90th-minute back-heel doubled the hosts' advantage, securing City's spot in the PL2 final.
Travis Binnion’s side had finished fifth in the regular season before knock-out victories over West Ham and Everton at Leigh Sports Village.
There’s now only one competitive game remaining for our Professional Development Phase (U17-U21) players. The Under-18s host Sunderland at Carrington on Saturday (12:00 BST), and you can watch live on MUTV.