Watford - Adam Bogdan's embarrassing blunder cost lacklustre Liverpool dearly as Watford swept to a 3-0 success that gave them their first home win over the Reds for 29 years.
Jurgen Klopp's side had only themselves to blame for Sunday's chastening loss at Vicarage Road and Hungarian goalkeeper Bogdan was the chief culprit after dropping a routine corner that Nathan Ake converted for Watford's early opener.
More calamitous defending, this time from Martin Skrtel, allowed Odion Ighalo to double Watford's lead and the Nigeria forward completed Liverpool's misery with his second late on.
Liverpool's performance was comically bad at times and ranked as the heaviest loss of Klopp's two months in charge.
The Reds are now without a win in their last three Premier League matches, leaving them five points off the top four heading into the hectic Christmas period.
While Liverpool are some way short of the finished article, Quique Sanchez Flores's Watford are enjoying their best season since the golden Graham Taylor era in the 1980s.
Even in a campaign already full of memorable performances, this was a landmark moment for Watford as they recorded their first victory over Liverpool since 1999 and their first on home soil since a John Barnes inspired win in December 1986.
The seventh-placed Hornets' fourth successive win lifted them to within one point of the top four and maintained the momentum of a remarkably strong showing in their first season back in the top-flight for eight years.
Klopp's preparations had suffered a late setback when Simon Mignolet was ruled out with a hamstring injury and Bogdan started in place of the Belgian goalkeeper.
Some cynics among the Reds travelling support might have claimed Mignolet's absence would actually be a boost to Liverpool given his shaky display in last weekend's draw against West Bromwich Albion.
But Bogdan quickly disabused them of that idea with a horrendous third minute mistake that gifted Watford the lead.
When Ben Watson curled over a corner, Bogdan appeared to have the ball in his grasp for what should have been a routine catch.
But, possibly distracted by Troy Deeney's near-post run, the Hungarian fumbled it and before he could regain full control as the ball bounced back towards him, on-loan Chelsea left-back Ake pounced to prod the ball over the line.
Bogdan protested that the goal should have been ruled out for Ake kicking the ball out of his hands, but referee Mark Clattenburg disagreed.
It was an awful start and there was worse to come for Klopp in the 15th minute as Ighalo doubled Watford's lead thanks to more pitiful play from the Liverpool rearguard.
Skrtel was the guilty party as Ighalo chased Troy Deeney's ball over the top and the Slovakian centre-back allowed himself to be bullied into a panicked, weak tackle.
Ighalo again showed more desire than his marker, seizing on the loose ball and driving a fine finish into the far corner for his 11th goal of the season and fourth in his last four games.
For once the sight of jubilant yellow and black clad supporters was unwelcome for Klopp, who enjoyed so many memorable days in those colours with his previous club Borussia Dortmund.
Bogdan still looked jittery and he almost presented Watford with a third goal when his limp punch hit a team-mate and had to be cleared off the line by Skrtel.
Bogdan finally made a positive contribution to deny Ighalo after more poor defending early in the second half.
There was slightly more thrust to Liverpool's attacking play after the interval, with Jordan Henderson forcing a fine stop from Gomes, who also denied Emre Can.
But it was hardly a tidal wave of pressure and the hosts surged forward one last time to make it three when Ighalo headed home Valon Behrami's cross in the 85th minute.