Swansea City's FA Cup involvement was brought to an end by Leyton Orient.
The League One side were able to add to their third round scalp of Norwich and progress to the last-16 of the competition.
Jimmy Smith opened the scoring 10 minutes before the break but Cedric van der Gun levelled shortly afterwards.
And despite dominating, the home side couldn't add to their single goal and were punished at the death when Alan Tate converted Paul M'Poku's cross into his own net.
Andrea Orlandi made his return from a thigh injury to start against Orient - but to occupy an unfamiliar role at left-back.
Youngster Daniel Alfei started his second FA Cup match in the other full-back position while Yves Ma-Kalambay took his place between the sticks.
The other changes saw Kemy Agustien and Cedric van der Gun come into the side to play in midfield and out wide respectively.
Swans: Yves Ma-Kalambay; Daniel Alfei, Ashley Williams, Alan Tate(C), Andrea Orlandi (Angel Rangel, 63'); Kemy Agustien (Stephen Dobbie, 69'), Joe Allen, Darren Pratley; Cedric van der Gun (Nathan Dyer, 87'), Scott Sinclair, Luke Moore.
Not Used:Dorus de Vries (GK), Albert Serran, Mark Gower, Craig Beattie.
Orient: Jamie Jones; Andrew Whing, Terrell Forbes, Ben Chorley, Charlie Daniels; Matthew Sping, Jimmy Smith, Stephen Dawson (C) (Adam Chambers, 64'), Dean Cox; Scott McGleish (Jonathan Tehoue, 46'), Alex Revell (Paul-Jose M'Poku, 80').
Not Used: Lee Butcher (GK), Elliot Omozusi, Tom Carroll, Harry Kane.
Referee: S Attwell (Warwickshire)
The Championship promotion race was cast to one side for the afternoon as the Swans focused their attentions on progressing in the FA Cup.
Leyton Orient upset the apple cart in the last round with a fine win at Norwich but Brendan Rodgers named a side he felt was good enough and strong enough to reach the last-16.
And the home side's intent was clearly there to see from the start as they started to stamp their authority early on.
Joe Allen split the defence with a pass that picked out Cedric van der Gun inside the area on three minutes, that was cut out to force the first of four corners inside the opening seven minutes.
Fellow midfielder Kemy Agustien had the chance to get his shot away moments later when he fired from 20-yards but O's 'keeper Jamie Jones tipped it past the post to safety.
Early indications showed that the former Everton youngster would be the busier of the two shot stoppers on a cold yet sunny afternoon at the Liberty, and on 16 minutes he had to get his body behind Scott Sinclair's strike after he cut in from the left.
It was all Swansea as far as keeping the ball was concerned and the hosts had further chances before the half-hour through Kemy Agustien, whose shot deflected wide, and Sinclair as he curled over from the edge of the box.
Luke Moore even came close to claiming his first Swans goal on 32 minutes; Agustien's precision picked out the run of Sinclair, his cross was aimed at Moore in the centre but Terrell Forbes just about managed to get the boot in and clear it.
But in football you have to turn your chances and possession into goals - and 10 minuteds before the break the home side were punished. Charlie Daniels delivered a free-kick into the heart of the area from the right and Jimmy Smith, who worked with Brendan Rodgers at Chelsea, got to the ball first to nod it beyond Ma-Kalambay.
That spurred the Londoners on to push for a second but as the fourth official was about to raise his board for added time the Swans struck. Ashley Williams picked out Pratley on the left, he crossed to find Moore and his flick was met by the head of Cedric van der Gun who helped it home.
Pratley thought he scored a second in stoppage-time but was flagged offside after touching in Sinclair's drive on the line.
Half-Time: Swans 1 Orient 1
The Swans made an explosive start to the start period and within two minutes of the re-start the home side almost made it two; Kemy Agustien and Cedric van der Gun playing a one-two and the latter was through on goal, but after pulling the trigger he called Jamie Jones into action to make an excellent one-handed save.
Daniel Alfei, Scott Sinclair and Agustien all screwed shots wide of goal in the proceeding minutes as the Swans continued to boss the start of the second-half.
But a fine move on 60 minutes almost brought a goal - Orlandi and Sinclair linking-up with the former volleying from close-range but saw it take a deflecion on the way. Unfortunately it was to be his final involvement of the afternoon and he was replaced by Angel Rangel.
Stephen Dobbie was thrown on in place of Agustien to provide extra fire power but that was after Sinclair saw another attempt deflect wide, this time off Andrew Whing.
The goals weren't as free flowing as they were in the last round against Colchester but the chances were still coming - Sinclair was inches away from poking home a second while Dobbie fired his first attempt of the afternoon across goal and wide.
The Scotsman came even closer eight minutes from the end when he turned and fired at goal and Jones pulled off an excellent acrobatic stop to deny him.
But such as the story in the first-half the Swans were punished by a rare Orient attack which brought a second goal, though they were handed a large piece of help. Substitute Paul M'Poku crossed from the right, Alan Tate went to clear it from underneath the crossbar but, instead, caught it completely wrong and sliced it into his own net.