Substitute Liam Cullen scored a superb late winning goal as Swansea City beat Portsmouth to land what could be a significant early blow in the battle for Championship survival.

After a first half of few chances, Pompey's Josh Murphy twice went close, before Swans winger Eom Ji-Sung had a fine 25-yard shot tipped over.

That sparked a period of pressure from the hosts, whose new head coach Vitor Matos used his bench to excellent effect as Zeidane Inoussa and Malick Yalcouye combined for fellow substitute Cullen to whip in a sumptuous first-time left-footed strike.

With fellow strugglers Oxford United conceding a late equaliser at Blackburn Rovers, Swansea's first back-to-back wins since April move them up to 18th in the Championship table, six points clear of the bottom three.

As for Portsmouth, a fourth defeat from five keeps John Mousinho's side 22nd, two points adrift of safety.

Despite coming at such an early stage of the season, this encounter carried an air of importance because of the two sides' lowly standing in the Championship.

Swansea's much-needed win over Oxford on Saturday had given Matos his first victory and snapped the Swans out of a five-game losing run.

That only took them up to 20th in the table, though, just two places and three points above Portsmouth, who had won only one of their previous nine matches.

Both sides started the game as if they were acutely aware of what was at stake – aggressive and pressing intently out of possession but reluctant to over-commit to any attack, wary of making what could be a costly mistake.

Scoring opportunities were scarce as a result, with Portsmouth's Conor Chaplin forcing Lawrence Vigouroux into a smart save and Swansea's Melker Widell denied by Pompey goalkeeper Nicolas Schmid.

Matos was quick to turn to the Swans' bench after the break as he brought on top scorer Zan Vipotnik and Cullen, but it was Portsmouth who went closest to scoring in the early stages of the second half with Murphy shooting wide and seeing another effort saved.

Swansea's substitutes soon got their team attacking with more purpose and pace, Vipotnik offering the front line a proper focal point and Inoussa creating problems for opponents with his direct running.

The Swedish winger had a big hand in the game's only goal, breaking down the left and passing to Yalcouye, whose attempt to control the ball fell kindly for Cullen to sweep in a sweet left-footed shot.

Swansea had their tails up and almost scored a second, with Ronald's powerful effort well saved by Schmid.

Portsmouth's late attempts to salvage a point amounted to little more than a volley over from Adrian Segecic as Mousinho's men missed the opportunity to close the gap on their relegation rivals.

Swansea head coach Vitor Matos:

"Mentality, desire, concentration, especially having good positioning in the game when we have the ball and when we don't have the ball, that is massive to get through these moments.

"The effort the team put in the first half, especially the midfielders, was unbelievable because that allowed us to stay competitive during the game.

"Then it's about details. It's about a brilliant shot from Liam, a good goal. We knew the bench would have massive impact on the game.

"So I'm really happy with the boys, really happy with the way we approached the game, and we know that we need to improve, we know that we need to play better with the ball…but I'm really happy."

Portsmouth boss John Mousinho speaking to BBC Radio Solent:

"The performance was really solid and the effort levels were there, we just switched off for the goal and didn't get the press right.

"There was nothing in the game but what is frustrating is that we got into some really good areas and just did not put Swansea under enough pressure.

"When we get into good areas we either don't shoot or the ball doesn't come into the area quick enough. With the players we have at the top of the pitch, we definitely have to be better.

"The major frustration for me was the goal. I could have taken coming away from here with a point."