Steve Cotterill suffered a nightmare return to Portsmouth as his Nottingham Forest side were thumped.
Cotterill quit to take over at Forest last month but saw his new side fall behind when Erik Huseklepp scored after Hayden Mullins had hit the crossbar.
Huseklepp then crossed for Dave Kitson to head in the second before the winger converted a pass from David Norris.
Pompey expect to appoint Cotterill's successor during the international break next week.
Lewis McGugan twice went close for Forest before Huseklepp - one of Cotterill's last signings for Portsmouth when he joined from Bari in August - broke the deadlock.
Mullins took aim from 25 yards a minute before the interval but the ball crashed off the crossbar and fell to Huseklepp.
He expertly curled the rebound past Forest goalkeeper Lee Camp into the top corner.
Luke Chambers came close to an equaliser when his header was cleared from off the goalline before Kitson doubled the lead.
Forest's misery was complete six minutes from time when Norris teed up Huseklepp to prod in number three.