Jaden Philogene and Chuba Akpom netted for Kieran McKenna's side at Portman Road.
Second-placed Ipswich, relegated from the top flight last season, are one point above third-placed Middlesbrough in the race for automatic promotion.
Middlesbrough were punished for failing to take their chances as Bobby Clark fired Derby to a 1-0 win at Pride Park.
The visitors dominated the game but lacked a ruthless edge and Clark took advantage with a second-half winner that condemned Middlesbrough to their third defeat in four matches.
Joe Rankin-Costello scored his first goal for Charlton as they drew 1-1 with leaders Coventry at The Valley.
Ellis Simms had put Frank Lampard's side ahead in the opening moments but Rankin-Costello's strike forced them to settle for a share of the spoils, leaving them eight points ahead of Ipswich.
Tom Ince's first league hat-trick in a decade gave fourth-placed Watford a 3-0 victory over Birmingham at Vicarage Road.
Millwall dropped out of the play-off places after a 0-0 draw at Southampton.
Thierno Ballo spurned a glorious late chance to win it for the Lions as Southampton's winless run extended to five games.
Stoke won 1-0 at fifth-placed Hull, while Preston, currently in the last play-off spot, beat bottom-of-the-table Sheffield Wednesday 3-0 at Deepdale.
Bristol City thrashed fourth-bottom Portsmouth 5-0 and third-bottom Norwich won 2-1 at QPR to move within one point of safety.