Roberto Firmino netted a hat-trick and Mohamed Salah scored another wonderful solo goal as Liverpool spoiled Claudio Ranieri's first game as Watford boss.
Firmino returned to the starting XI with three tap-ins, with the last coming in stoppage time.
Salah's jinking run and finish - reminiscent of his goal against Manchester City - was his side's fourth in what was a magnificent display.
Sadio Mane's 100th Premier League goal had given the Reds the lead.
Jurgen Klopp's side remain unbeaten in the league and are now two points clear at the top of the Premier League, but have played a game more than Chelsea, who face Brentford later on Saturday.
Need a VPN? Or seeking to switch? Then support Tribal Football by clicking here to sign up with our official partners NordVPN. Not only will you receive the best VPN experience, but also great discounts by signing up via Tribal Football. Thanks for your support!