Paul Cook shrugged off the disappointment of a late Stevenage leveller as Pompey remained in second spot.
Conor Chaplin climbed off to bench to net what appeared to be a 77th-minute winner at Fratton Park tonight.
But another substitute, Brett Williams, headed home Charlie Lee’s long throw deep into stoppage-time to claim a 1-1 draw.
The result denied Pompey returning to the top of League Two, yet they continue to possess only one defeat in their opening 14 league fixtures.
Cook said: ‘To have won tonight would have seen us go to the top of the league.
‘The gap over the play-offs is getting higher and higher and everyone wants that big advantage.
‘We are all disappointed. My job as manager is to manage the disappointment alongside the highs.
‘As much as we are disappointed I don’t think the players have done a lot wrong tonight.
‘We have been undone by a long throw with a couple of big lads in the box we haven’t dealt with.
‘We take that on the chin and we move on to Mansfield but we have lost once in our first 14 matches so shouldn’t forget that.’