England Under-21 striker Darren Eadie fired home a close-range winner as Norwich came from behind to plunge Portsmouth closer to the relegation zone.
The home side had taken the lead on 29 minutes when Australian John Aloisi side-footed home his 16th goal of the season at the near post.
But striker Iwan Roberts gave Norwich a deserved equaliser seven minutes into the second half, firing inside the right-hand post to finish off the best move of the match.
Roberts was then unlucky to see a header cannon off the crossbar to safety, as Norwich pressed forward for the second goal.
And Eadie took advantage of a dreadful defensive mix-up in Portsmouth's six-yard area to race in and bundle home the ball from close range.
The defeat was Portsmouth's fourth in a row and they have now failed to win in their last nine matches but they had started the better in the first half, and Aloisi should have given them the lead in the 17th minute.
The Australian striker found himself clean through on goal as the Norwich defenders appealed for offside, but goalkeeper Andy Marshall came to the Canaries' rescue as he blocked Aloisi's shot with his legs.
But the 22-year-old forward made amends 12 minutes later when he underlined his growing potential by firing home his 13th goal of the season.
Jamaican Fitzroy Simpson did well to cross the ball from the by-line allowing Aloisi to nip in at the near post and stroke the ball past a helpless Marshall.
Norwich came back strongly and were unlucky not to have drawn level by half-time with Roberts and Craig Bellamy both sending headers crashing against the woodwork, while the former also had a goal disallowed for pushing four minutes from the break.
But Norwich came out in more determined fashion in the second half and were level within seven minutes of the restart through the best move of the match.
Defender Daryl Sutch played the ball forward to Eadie who cut inside before threading a ball forward for Roberts to beat outstretched keeper Alan Knight from 15 yards.
Roberts was unlucky seven minutes later when he powered a header against the bar only for it to roll along the goal line to safety, but Eadie was on hand in the 73rd minute to give the visitors a deserved lead.
Aloisi, who was a handful for Norwich's defence all night, wasted two golden chances to bring his side level in the closing stages.
The striker forced a brilliant full-length save from Marshall in the 88th minute when his shot looked destined for the top corner.
But he was guilty of indecision in injury time with just Marshall to beat allowing Norwich captain Matt Jackson to make a goal-saving tackle to secure the points.