The goalkeeper's second-half error pushed his side closer to the trapdoor as the hosts recorded a vital victory at the Liberty Stadium
Brad Guzan's error helped Swansea City to further ease their Premier League relegation concerns as they claimed a 1-0 win over rock-bottom Aston Villa.
The Villa goalkeeper came out meet Gylfi Sigurdsson's free-kick eight minutes after the break but could only swat the ball on to the onrushing Frederico Fernandez, who bundled into the net.
The visitors were left to rue several missed opportunities in the first half, with Rudy Gestede seeing a spectacular overhead kick denied by an Ashley Williams block after Joleon Lescott and Jordan Ayew spurned earlier chances.
Swansea held on and made Villa pay for their profligacy just after the break, condemning the visitors to a 21st defeat of the campaign – sealing their worst return in the Premier League after a turbulent week off the field.
The result will place more pressure on Villa boss Remi Garde, who was linked to a return to former club Lyon over recent days, with his side now 12 points behind fourth-bottom Norwich City - victorious earlier on Saturday at West Brom - and seemingly condemned to Championship football next season.
In contrast, the win sees Swansea pull 11 points clear of the drop zone, meaning only a spectacular collapse will see them lose their top-flight status.
Head coach Francesco Guidolin, returning to the Swansea dugout after a three-match absence due to illness, made three alterations to his side, but will have been disappointed by his team's start at the Liberty Stadium.
A poor clearance from rookie left-back Stephen Kingsley allowed Lescott to fire just wide in the third minutes, before Ayew blazed over from 18 yards six minutes later.
Gylfi Sigurdsson's corner was glanced wide by Jack Cork as the hosts sought a response, while a Jordan Vertout set-piece at the other end saw Ciaran Clark guide a free header over the bar on 22 minutes.
Garde's men, who have now picked up just three points from the last 45 available on the road, continued to look the most likely to break the deadlock.
Gestede powered a header straight at goalkeeper Lukasz Fabianski in the 33rd minute, before seeing his acrobatic attempt well blocked by Williams – the Swansea captain with whom he was earlier involved in a heated on-field tussle.
And Villa were made to pay for those missed chances in the 53rd minute as Guzan palmed a curving Sigurdsson free-kick straight to Fernandez, who deflected home.
A largely uneventful second half saw the visitors continue to enjoy the majority of possession, but Lescott's header at Fabianksi – making his 100th Premier League appearance - 17 minutes from time was as close as an equaliser came.
Late Swansea nerves could not prevent Villa from suffering a sixth straight defeat and Bafetimbi Gomis should have sweetened the win in stoppage time but drilled a 25-yard drive past the post following a sweeping counter-attack.
- Goal