Brighton fell behind when goalkeeper Bart Verbruggen inexplicably spilled Cole Palmer’s tame effort into the net.
Georginio Rutter quickly headed Albion level before a fine finish from Mitoma, who was subject of a failed bid from Saudi Arabian club Al-Nassr during the transfer window, settled the all Premier League tie with 57 minutes played.
Their reward for beating the Blues was another all-Premier League tie as they face a 700-mile round trip to face Eddie Howe’s Newcastle United, who advanced to the fifth round thanks to their 3-2 victory at Birmingham City last weekend.
Elsewhere, Plymouth’s reward for beating Liverpool in the FA Cup is a fifth-round tie away to Manchester City.
The Pilgrims dumped the current Premier League leaders out of the competition with a 1-0 win on Sunday, and will now head to the Etihad Stadium for a last-16 tie on the first weekend of March.
Cup holders Manchester United will face Fulham after beating Leicester in controversial circumstances while there are also all-Premier League ties between Bournemouth and Wolves.
Fifth round draw in full: Preston v Burnley, Aston Villa v Cardiff, Doncaster or Crystal Palace v Millwall, Manchester United v Fulham, Newcastle v Brighton, Bournemouth v Wolves, Manchester City v Plymouth, Exeter or Nottingham Forest v Ipswich.
