Substitute Kal Naismith ensured Portsmouth maintained their push for the Sky Bet League Two play-off spots after his late strike secured a 2-0 win away to Stevenage.
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.