A key figure in the Blues' League Two title-winning side, the experienced midfielder was back at Fratton Park on Monday with Wigan.
The visit of the high-flying Latics also marked returns for ex-Pompey boss Paul Cook and striker Noel Hunt.
Roberts was given a standing ovation by supporters in the South stand and Fratton end while warming up during the first half, with his name also sung.
Then, as an 81st minute substitute for Michael Jacobs, he was given a tremendous reception by home supporters as he entered the pitch.
The 34-year-old subsequently provided the cross for Will Grigg's 89th minute consolation goal for the visitors.
Yet the fan reaction on the evening touched Roberts, who has tweeted in response to the subject being raised.
He posted: 'Unbelievable!! Was taken back by it, totally unexpected'.
Roberts totalled 80 appearances and 20 goals during a two-year Pompey stay.
However, he was subsequently made surplus to requirements by new boss Kenny Jackett and departed by mutual consent in August.