Two Swansea goals came in an excellent first half for the home side, Andre Ayew opening the scoring before Jack Cork doubled the lead.
Christian Benteke's half-time introduction had some impact, the Belgian heading in from a corner with 20 minutes of the second half played. However, things were to again get worse for the Merseysider's, Ayew getting his second of the game before Brad Smith was sent off.
Changes do little to inspire Reds
Jürgen Klopp made eight changes to the Liverpool team that were beaten by Villarreal on Thursday, with Nathaniel Clyne, Dejan Lovren and Philippe Coutinho the only survivors.
It was clear from the start that the inexperienced side were going to struggle, Swansea threatening early on. Sloppy play from Daniel Sturridge saw the striker give the ball away, allowing Jefferson Montero to set up eventual goalscorer Ayew. Luckily for Liverpool, he blazed over on the half volley.
They weren't so fortunate minutes later, Swansea scoring from a corner after Lovren blocked a goalbound effort from Ayew. It was that man who scored from the corner, heading in without much trouble after losing his man inside the six yard box.
Corker from Cork
From the on in, Swansea kicked on. Danny Ward kept his side in it for a while, making crucial saves from the likes of Gylfi Sigurdsson, but he could do nothing about the second goal.
Jack Cork was allowed far too much room in the midfield after Liverpool gave the ball away cheaply once more, marauding forward before curling the ball perfectly into the corner of the net from 20 yards out.
Klopp wasn't happy, taking off Pedro Chirivella and Coutinho off at the break, Lucas and Benteke the replacements.
Ojo brightest in dark display
The Reds did show signs of an improvement as the game got back underway, Sheyi Ojo continuing to impress again, as he has done in a few cameo appearances this season. He almost helped Liverpool earn a penalty, crossing for Benteke, who was seemingly pulled down. Nothing was given by referee Roger East.
Benteke didn't let that affect him though, heading in from a corner to make it 2-1 soon after. He broke free of his man, getting ahead of teammate Kevin Stewart and onto the end of Ojo's corner.
Benteke's goal was no catalyst for comeback
Unfortunately for Klopp's men, the Swans replied instantly, Ayew again the tormentor. It was a combination of errors that led to the Ghana international scoring, eventually fumbling the ball into the corner of the net after it landed kindly for him in the penalty area.
Things went from bad to worse, not long after, as Brad Smith was sent off. Booked in the first half, Smith knocked Kyle Naughton over as the full-back looked to counter from a corner, leaving East with no decision but to show him a red.
From then on it was easy for Swansea, who were only too happy to keep the ball off Liverpool, easing to victory. The Reds' attentions now turn to Thursday's second leg against Villarreal, hoping to overturn the 1-0 defecit.