Roberto Firmino ended his Premier League goal drought as 10-man Liverpool maintained their unbeaten start at Watford.
The striker headed in late on to complete a 3-0 win and score his first top flight goal since 15 September.
Trent Alexander-Arnold's brilliant free-kick had made it 2-0 after Mohamed Salah opened the scoring after the break.
But Liverpool will be without Jordan Henderson for next weekend's Merseyside derby with Everton after he was sent off for two bookings.
Hard-working Watford will feel aggrieved after Jon Moss rejected their penalty claims when Andy Robertson tripped Will Hughes in the second half with the score level.
It was far from a vintage Liverpool performance but they remain unbeaten in 13 games and two points behind Premier League leaders Manchester City.
The hosts began brightly but Gerard Deulofeu's early strike was correctly ruled out for offside.
The former Everton loanee then fluffed his lines when Liverpool gifted Watford possession on the edge of the area.
Liverpool had scored 17 goals in their previous five games against the Hornets but struggled to seriously threaten.
Ben Foster tipped Xherdan Shaqiri's cross away from the lurking Salah, then Georginio Wijnaldum missed his kick.
Firmino had scored just once in his previous 14 games with Salah netting one in his last three outings and Mane notching three in 12.
All three had quickfire chances before the break but Foster was equal to them.
First, he saved low from Firmino after 38 minutes before turning Mane's acrobatic effort behind four minutes later.
From the resulting corner Salah rose unchallenged but Foster gathered his header.
In the midst of Liverpool's flurry of chances Alisson was forced to turn away Roberto Pereyra's drive.
It was an energetic end to an ultimately disappointing half but Watford upped the tempo after the restart and were furious they were not awarded a penalty on 56 minutes.
Robertson clipped the incoming Hughes after losing track of the ball and, while the midfielder went to ground easily, Watford's complaints looked justified.
And the hosts' frustrations would not have eased 11 minutes later when Salah broke the deadlock.
Firmino fed Mane on the left and the forward crossed for Salah's instinctive shot from eight yards to clip Craig Cathcart and squirm through Foster.
Deflated, Watford did not recover from the setback and Alexander-Arnold added an excellent second 14 minutes from time.
Firmino was fouled 25 yards out and the England international curled a brilliant effort over the wall and past the static Foster.
The hosts were given hope when Henderson was dismissed for a second yellow card when he clattered into Etienne Capoue with eight minutes left.
But Firmino headed in after 89 minutes when Foster denied Mane to complete the victory.