Roberto Firmino scored a hat-trick as rampant Liverpool condemned Claudio Ranieri to a miserable start to life as Watford manager in a one-sided game at Vicarage Road.
The home side had no answer to Liverpool's fluid attacking play.
Sadio Mane became the third African player to score 100 Premier League goals before Roberto Firmino struck either side of the break and Mohamed Salah finished a brilliant individual goal with a smart shot beyond Ben Foster.
Firmino completed the scoring in the final minute for his first hat-trick since December 2018.
The result means Liverpool have scored three goals or more in all six away games in all competitions so far this season, something no other English top-flight side has ever managed. It also extended their unbeaten start to the season and took them back to the top of the table, before Chelsea's visit to Brentford (17:30 BST)
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Watford did not manage a corner until the 78th minute. That it was greeted with huge cheers and a standing ovation just about summed up Ranieri's day.
Source: BBC