Former Southampton striker Connolly gave Pompey the lead in the 22nd minute with a clever glancing header from a curling Jed Wallace free-kick.
But the home side's hopes of celebrating a first victory since October lasted just five minutes before defender Shaun Williams struck a brilliant equaliser.
Williams controlled Daniel Powell's right-wing cross neatly in his stride before flicking the ball up and unlesahing an unstoppable volley into the top corner from 12 yards.
Dons striker Izale McLeod endured a frustrating return to his old club, passing up a host of good opportunities before being substituted just 15 minutes after half-time.
McLeod could have opened the scoring after just 16 minutes when Pompey defender Ricardo Rocha played a clearance straight to the feet of his old team-mate but the striker blazed wide.
Things got even worse for McLeod at the start of the second half when Powell floated in a delightful cross and he somehow failed to make contact with the ball with an attempted header from six yards.