The Reds came into the game having drawn four of their last five outings in all competitions, form that had prompted questions over their title credentials.
However, the hosts answered those in fine style at Anfield, finding their scoring touch again through braces from Virgil van Dijk and Sadio Mane and a further goal from Divock Origi.
Manchester CIty’s hard-fought win over West Ham United ensured the night wasn’t perfect for Liverpool, but there was plenty to encourage fans ahead of a Merseyside derby trip to Everton this weekend.
Jurgen Klopp made two changes to the XI that was held to a 0-0 draw at Manchester United on Sunday, with Trent Alexander-Arnold and Origi taking the places of Jordan Henderson and Roberto Firmino.
And it didn’t take long for the manager’s decisions to be vindicated.
Just nine minutes had elapsed when restored right-back Alexander-Arnold fired a dangerous cross toward Mane, playing centre-forward in the absence of Firmino.
The Senegalese made no mistake with the finish, either, showing spring-loaded heels in getting over the ball to head into the far corner.
The right-hand side – Watford’s left – continued to prove fruitful for the Reds, with Mohamed Salah twice sending Alexander-Arnold into the box to for crosses that required desperate Watford defending.
But the Englishman would not be denied, and was again the provider from the right wing as Mane netted his second.
The No.10 looked offside such was the timing of his run, but the flag stayed down, allowing for a brilliantly improvised backheel that left Ben Foster with no chance.
Mane almost had his hat-trick before the break, coming within inches of finishing a fine team move involving Origi and Salah and ending in an agonisingly overhit Andy Robertson cross.
Watford had carved out enough promising moments on the counter in the opening 45 minutes to believe that they could make things interesting by grabbing the first goal of the second half.
However, the Reds simply picked up where they left off, dominating the ball and forcing the visitors into their own box.
When the Hornets did manage to get close to the opposition goal, their chance fell to arguably the wrong man – defender Craig Cathcart volleying a shot into bodies when it had dropped fortuitously into his path.
Regardless, it wasn’t long until the hosts were back at the other end of the field, and this time they made it count.
Origi, who had already justified his inclusion with a busy performance on the left, further underlined his value by cutting in off the wing and driving a low shot goalward.
And with the Hornets’ resolve finally broken, fans at Anfield were treated to the Van Dijk show.
First, the Dutchman rose highest to nod home a right-sided free-kick that represented Alexander-Arnold’s third assist of a productive night.
Then, he stayed put after another set-piece was cleared, waiting for another fine cross from Robertson that was greeted with the header it deserved.
The scoring finally stopped there for Liverpool, but there was joy from the Anfield crowd as they revelled in the perfect preparation for the Merseyside derby on Sunday.
