The Tigers were edged out of the automatic promotion places by Leicester after their 1-0 home win over Middlesbrough on Friday night but it looked like Steve Bruce's team would leapfrog the Foxes after Joe Newell's first-half own goal put them ahead.
However, Peterborough saved themselves from a 10th home league loss 11 minutes from time when McCann scored from the spot.
It meant Posh drew a league game at London Road for the first time since April 21.
Jaanai Gordon-Hutton made his first league start for the hosts.
The 17-year-old's inclusion at the expense of Kane Ferdinand, who began the game on the bench, was the only change made by manager Darren Ferguson following last weekend's defeat at Nottingham Forest.
David Stockdale returned to the Hull side as one of four changes made by boss Bruce.
Stockdale re-signed for the Tigers this week after heading back to parent club Fulham in December. He replaced Eldin Jakupovic in goal.
David Meyler and Robert Koren came back into midfield after missing the FA Cup replay win at Leyton Orient in midweek along with forward Robbie Brady. Andy Dawson, Corry Evans and Tom Cairney made way for the returning trio.
Dwight Gayle was unable to add to the 10 goals he has scored for Peterborough since his arrival on loan from Dagenham & Redbridge at the end of November when he headed wide after eight minutes.
Gordon-Hutton threatened with a shot from the edge of the area shortly afterwards before Brady did likewise at the other end midway through the first half.
Liam Rosenior, Nick Proschwitz and Paul McShane all had headers at goal before the half-hour mark - but Posh did not heed the warnings and fell behind in the 31st minute following another cross into their box.
Koren whipped his corner in at the near post and Newell inadvertently diverted the ball past Robert Olejnik.
Gordon-Hutton and on-loan Manchester United youngster Davide Petrucci, making his home debut, went close with efforts from outside the area either side of the half-time whistle.
Stephen Quinn replied for Hull just before the hour and the enthusiastic Gordon-Hutton sent in another shot with 15 minutes remaining.
The hosts equalised after 79 minutes from the penalty spot after Tommy Rowe was brought down by Tigers defender James Chester.
The in-form Gayle wanted to take the spot-kick but McCann took the ball off him and stroked his shot past Stockdale.
Peterborough survived a late scare when substitute Cairney swung in a corner and McShane's diving header had to be parried away by Olejnik.
- Sports & Recreation