The travelling 500 or so Posh fans will have been happy at half-time on Saturday after watching Lee Tomlin's sixth goal of the season hand them an eighth-minute lead.
But it was not enough to claim all three points as Tomlin turned villain on the hour as he brought down Lee Martin in the penalty area, leaving on-loan QPR striker DJ Campbell to equalise from the spot with what was Town's first shot of the match.
The visitors, having lost their last four, were the better side on the overall balance of play and will be much happier with the point, although the two sides now prop up the second tier after Bristol City's surprise win at Middlesbrough.
Tyrone Barnett was ineligible for Ipswich following his loan move from Peterborough in midweek, with Town boss McCarthy opting to make just two changes after last weekend's 6-0 mauling at Leicester with Tommy Smith and Michael Chopra coming in.
Posh were also heavily beaten last time out, losing 4-1 at home to Blackburn, and Darren Ferguson tinkered as fit-again Mark Little and loan signing George Thorne came in.
A dreadful first half was punctuated only by Posh's eighth-minute opener, deserved reward for their better showing. Tomlin received the ball from Joe Newell on the left and, amid terrible defending from Danny Higginbotham and Aaron Cresswell, finished calmly right-footed into the bottom corner from 12 yards.
Saido Berahino enjoyed only the second shot of the first half in the 43rd minute but his effort was easily collected by Stephen Henderson.
Ipswich were handed the chance to draw level on the hour mark as Martin was brought down in the area by Tomlin, and Campbell stepped up to draw level with a well-taken spot-kick.
Tomlin was presented with a chance to redeem himself soon after but Henderson saved well, while Campbell came within inches of putting Ipswich ahead at the other end.
Little fired narrowly over for Posh in the 68th minute before substitute Dwight Gayle, making his debut after arriving on loan from Dagenham and Redbridge, enjoyed two good chances after Martin had tested Bobby Olejnik.
Olejnik made a smart save to keep out Higginbotham's late header before Henderson denied Grant McCann.