Hermann Hreidarsson’s 24th-minute strike, his first goal since 2009, secured Pompey a sixth straight win which keeps their slim play-off hopes alive.
The beleaguered Blades, however, remain in the Championship relegation zone six points from safety.
Adams, who has yet to taste victory in 13 matches since taking over from Gary Speed in December, felt his side deserved to come away with at least a draw.
Adams said: “Nicked a point? I think that was the least we deserved, but once again it’s a fine line between success and failure. We’ve seen that again.
“We conceded a goal from a corner and for long periods of the game we had Portsmouth pinned back without it falling for us.”
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