Jason Scotland looked to have given Ipswich a fourth straight win with an 82nd-minute goal against the run of play.
But Mellis combined with substitute Kieran Trippier to apply the finish in stoppage time that gave Mark Robins' team a deserved share of the spoils.
The clash had offered little in the way of quality and a draw was a fair reflection of two teams stuck in the division's middle reaches.
Source: PA
Source: PA