Matty Godden scored two goals to reach 21 goals this season and helped Charlton secure the fourth spot in League One with a 3-1 victory over Burton Albion.
Charlton, who haven't lost in 15 consecutive matches at The Valley, are set to play against Wycombe in the play-off semi-finals.
Burton Albion took the lead in the 13th minute after Mason Bennett successfully converted a penalty kick following Fabio Tavares' foul by goalkeeper Ashley Maynard-Brewer.
Godden equalized in the 24th minute, finishing from the right side of the penalty box as Burton keeper Max Crocombe made a mistake by coming off his line in an attempt to intercept Tennai Watson's pass.
Godden extended Charlton's lead in the 34th minute with a quick turn after receiving a pass from Josh Edwards, beating Crocombe with a low shot on his left foot.
Alex Mitchell, who was at fault for the early penalty, redeemed himself by scoring a header from Conor Coventry's corner in the 51st minute, putting Charlton 3-1 ahead.
Charlton's new player Ibrahim Fullah hit the right post after a pass from Karoy Anderson.