Ethan Galbraith and Josh Key's goals pushed Portsmouth towards the Championship relegation fight as Swansea boosted their play-off hopes with a 2-1 away victory.
Galbraith and Key both scored eye-catching goals from the edge of the area as the Swans belied their away day woes with their first league victory at Fratton Park since 1959 to move within five points of the play-off places.
Jacob Brown netted for the first time in 13 months but it only proved a consolation, as Pompey sit four points ahead of the relegation zone, and could be closer after Wednesday's fixtures.
The Championship's leading goalscorer Zan Vipotnik had two early chances to add to his 17 strikes already this season.
The first came from the right where he skied a low cross over the bar, before he could not keep his header down after a delivery from the other flank.
Portsmouth did not offer much in the first half, but had the first golden chance after a clever corner routine found Jacob Brown on the edge of the box. The forward saw his first-time effort pushed on to the post by Lawrence Vigouroux - with the rebound falling perfectly in the goalkeeper's hands.
In the 26th minute, the visitors claimed the lead through a wonderful Galbraith finish, but it owed much to a fantastic build-up.
Lawrence Vigouroux's stunning 70-yard diagonal picked out Eom Ji-sung before Josh Tymon recovered from a blocked shot to lay off to Galbraith - who curled home for his fourth goal of the season.
It took just 13 minutes for the Swans to double their advantage when Key was given plenty of time and space on the edge of the box to loop over Nicolas Schmid, with the aid of a deflection.
The home fans were disapproving of the first-half performance and booed the players off at the interval.
Galbraith had two contrasting chances to add a third. The first an opportunistic blast from the halfway line, which nearly caught out Schmid, and then a drag across goal when clean through.
Pompey had lost their previous two home matches without scoring, with three blanks in a row not seen at Fratton Park since 2008.
Chaplin thought he had ended the drought when he steered in, but the ball had already gone out of play in the build-up.
And the barren run was finally beaten in the 66th minute when Brown headed in Zak Swanson's cross for his first goal since arriving from Luton.
John Swift and Swanson both forced Vigouroux into saves with stoppage-time headers but Pompey could not salvage a point.
Portsmouth's John Mousinho:
"We were really poor in the first half and much improved in the second. We nearly got ourselves back into it but we gave ourselves too much to do.
"It is very disappointing. You think where was the intent in the first half? Where was the aggression and front-footedness?
"Pretty much everything went wrong. We were a couple of yards off everything. Regardless of how good Swansea were good on the ball, we didn't do much right.
"It was like the first time we had seen a ball in the first half. We gave it away relentlessly.
"I don't think the Sheffield United and Hull defeats are too much of an issue.
"I thought we dominated both those games and were unlucky not to come away with more.
"Tonight was the first time we have played as poorly as that. We didn't put in a proper home performance in the first 45 minutes.
"Regardless of whether you are playing home or away, you can't perform like that."
Swansea's Vitor Matos:
"I think we have had some good away performances without getting the points.
"We needed to improve to win games away and we have been trying. Today the mentality, resilience, organisation and performance were there.
"I am really happy for the club, the team and the fans.
"We expected Portsmouth to fight back. It is not an easy place to come and Portsmouth have a lot of weapons.
"Putting on pressure and controlling the space in behind is not easy so towards the end the fatigue hit and the bench was important to help the team.
"Some games you have to win it with more than controlling the ball and I think we did that today.
"When you have a 2-0 game it can be quite tricky as it can turn quickly.
"The first half was a very good performance."
