Stefano Okaka headed home from a corner to give Watford an early lead and Abdoulaye Doucouré later restored Watford’s advantage after Sadio Mané had equalised for Liverpool with a superb goal.

José Holebas delivered an inswinging corner from the right and the shortcomings of Liverpool’s zonal marking system were brutally exposed when Okaka directed a free header beyond Simon Mignolet, with Dejan Lovren caught in no man’s land and Firmino also guilty of allowing the Watford striker to drift past him too easily.

Okaka, who is built like a heavyweight boxer, caused Liverpool no end of problems in the first half with his physical presence in front of a Watford midfield that snapped into tackles and denied Klopp’s team the time and space to impose themselves.

Alberto Moreno, who was preferred to James Milner at left-back and given his first Premier League start for 10 months, swapped passes with Mané on the edge of the Watford area before sliding a low ball into the feet of Emre Can.

Tom Cleverley got away from Jordan Henderson in the inside-right channel and delivered a low centre that pinballed between Trent Alexander-Arnold and Joël Matip, leaving Doucouré with the simple task of sweeping home from six yards out.