Liverpool had it all set up to move five points clear of fifth-place Tottenham, but instead, the Reds showed their inconsistency in a shocking defeat at Swansea.
Alfie Mawson's first half goal gave bottom side Swansea City a shock win over Liverpool, who had an unusually frustrating night in front of goal on Monday night.
The first half was a tense affair, with the first real chance coming when Mohamed Salah was played in by Virgil van Dijk, but the Egyptian uncharacteristically fired his volley over.
Prior to that, Van Dijk had gone close with a header from an Alex Oxlade-Chamberlain corner, while the former Arsenal man had also tested Lukas Fabianski with a half volley from just outside the box, as the visitors controlled the game but failed to find the end product in the final third.
Despite creating nothing for most of the first period, it was the hosts who took a lead into half time when a loose ball from a corner dropped to Alfie Mawson inside the penalty area, and the center back fired home with the home side's only shot on target in the first half.
Around 30 seconds before the halftime whistle, the Reds should have leveled when Sadio Mane found space during a blistering counter attack and was put through from Salah's cross. However, the Senegal winger appeared to lose his footing and his volley was scuffed wide.
Despite the surprise scoreline, the second half began very much in the same vein with Liverpool dominating the ball and had half chances within the first 10 minutes of the restart, though the Reds could not truly test Swansea keeper Fabianski.
Their dominance continued and Fabianski started to receive more tests, but had the answers with quality saves to deny Salah and then substitute Danny Ings. The Reds seem to be mainly restricted to long range efforts with Joel Matip, Joe Gomez and then Virgil van Dijk all firing wide from around the 25-yard range.
Carlos Carvalhal's side offered little going forward, but defended resolutely as Jurgen Klopp's Liverpool labored to find ways through, but it was quickly becoming clear that a week after their spectacular win over Manchester City, it wasn't going to be their night.
The last chance of the game in a bitty and disjointed second half fell to Roberto Firmino. Swansea hearts where in mouths as it looked as though the Brazilian forward has saved a point with his late header from close range, but somehow his effort hit the post, while Adam Lallana's rebound attempt was blocked.
Despite Liverpool having 72% of possession and 21 efforts on goal to Swansea's three, even the unusually out of sorts Salah could not find the target in a bitterly frustrating night for the Reds, who suffered their first defeat since October. The defeat was only their third in the league all season, and keeps them fourth, two points clear of fifth-placed Tottenham.
For Carvalhal and Swansea, however, the victory is a huge three points in their quest for Premier League survival and just their fifth win of the season.
The Swans now move level on points with 19th-placed West Brom and are three points away from safety.