Now heading into a semi-final, Chelsea seemed dead and buried four minutes after half-time when Forest took a 3-0 lead, but it was soon to change.
Ex-São Paulo man Piazon produced a neat turn and shot to put Chelsea back in contention before his team-mates completed the victory.
A full report can be found here.
Chelsea (4-2-3-1): Jamal Blackman; Todd Kane, Nathaniel Chalobah (c), Nathan Ake, Adam Nditi; John Swift, Lewis Baker (Alastair Gordon 89); Reece Mitchell (Archange Nkumu h/t), Amin Affane (Alex Kiwomya 73), Lucas Piazon; Islam Feruz
Unused substitutes: Mitchell Beeney, Anjur Osmanovic
Nottingham Forest (4-4-2): Dimitar Evtimov; Lawrence Gorman, Jamaal Lascelles, Kieran Fenton, Jack Andrews; Michael Holligsworth (Wilfried Gnahore 84), David Morgan, Jack Blake (Derrick Otim 89), Ben Osborn; Jordan Palmer-Samuels, Kieran Wallace
Unused substitutes: Jordan Smith, Elliott Ackroyd, Aristote Kamaneno
