Naismith had only been on the pitch for 11 minutes when he was played in on goal by Kyle Bennett and fired past Boro goalkeeper Jamie Jones
His change was part of a double switch in attack, coming on with Michael Smith, to replace the excellent Gary Roberts and Mark McNulty, who had challenged Stevenage's defence all afternoon
It was that combination who had given Portsmouth the lead on 21 minutes, Roberts sliding a ball through for McNulty to add his 10th goal of the season
On 57 minutes Roberts was denied at close range by Jones, who was called into action a minute later to tip Michael Doyle's long-range strike over the bar
Portsmouth dominated but Tom Conlon came close on four occasions for Boro, thumping one effort onto the crossbar late on, while Tom Pett's goalbound strike was blocked by his own teammate Byron Harrison on 61 minutes
Source : PA
Source: PA