Slack marking allowed Ash Taylor to head in-form Tranmere in front, but Pompey equalised through Gabor Gyepes just after half-time.
Ronnie Moore's team, who drew with Stevenage last time out, thought they had done enough to win the game when Michael O'Halloran scored 16 minutes from time, but Jake Jervis equalised 60 seconds later to make it 2-2.
Doncaster were unable to capitalise on Tranmere's slip up, though, as their four-match winning streak came to an end with a 1-1 draw at Swindon.
Matt Ritchie's first goal of season of the season gave Paolo Di Canio's side the lead, but a Danny Hollands own goal made it 1-1.
Ryan Flynn, Nick Blackman and Neill Collins were all on target as Sheffield United moved up to third with a 3-1 win at Carlisle, for whom Danny Livesey scored a second-half consolation.
Brentford also moved up the table into fourth after extending their unbeaten run to eight matches with a 3-2 win over MK Dons.
The Dons, who beat Wimbledon in a highly-charged FA Cup match last weekend, went 1-0 up courtesy of Ryan Lowe's fourth of the season, only for Clayton Donaldson to equalise. Stephen Gleeson put Dons ahead again, but Harry Forrester made it 2-2 and Donaldson wrapped up the win with a last-minute poacher's effort.
Notts County dropped out of the playoff positions with a 0-0 draw at Yeovil while Crawley fell to 10th after drawing 2-2 with strugglers Shrewsbury.
Josh Simpson scored twice for Crawley, but his goals were cancelled out by strikes from Matt Richards and Jon Taylor.
Cyrus Christie was on target while Carl Baker and David McGoldrick both bagged a brace to help Coventry to a comfortable 5-1 win over neighbours Walsall at the Ricoh Arena while Crewe won 3-1 at Preston thanks to goals from Luke Murphy, Bradden Inman and Mathias Pogba.
Hartlepool's winless run now stands at 18 matches after Stevenage ran out 2-0 winners at Victoria Park thanks to goals from Marcus Haber and Lucas Akins, while second-from-bottom Scunthorpe also lost 2-1 at home to Bournemouth.
Leyton Orient kept up their impressive unbeaten run with a 2-0 win at Bury, while Oldham condemned Chester to a defeat by the same scoreline at the Weston Homes Community Stadium.