Mohamed Salah and Roberto Firmino were both on target for the Reds but neither will want to add their goal to their highlight reel.
A largely mediocre performance from Liverpool with two scrappy goals split by a brilliant free-kick, it was enough to take the points for the title chasers though.
It was an entertaining stalemate for the first 45 minutes, as Liverpool dominated possession but Watford always offered a threat. It was a game played a very high tempo with both sides heavily utilising the pace of their forwards.
The final ball was unfortunately too often lacking for both sides which made clear-cut chances few and far between despite the energetic end-to-end pace. It was Roberto Pereyra who came closest to breaking the deadlock for Watford, forcing an excellent save from Alisson Becker.
But Ben Foster was every bit his opposition number's equal to deny Salah from the unlikely source of a corner as the teams went in level at halftime.
The pace died down a bit as the game went on, and the two sides became caught in the mire of a stalemate. It was perhaps a fitting the underwhelming finish but Liverpool's talisman delivered again, putting his side one-nil up in the 67th minute.
It was the kind of goal we've seen a million times from them, Firmino to Sadio Mane who squared the ball for Salah to slot home. Foster should really do better with the tame effort considering some of the saves he'd already produced in this game, but it would be harsh to be too critical.
There was nothing Foster could do just nine minutes later though as Trent Alexander-Arnold whipped a spectacular free-kick into the top corner to put the game beyond all doubt. Firmino rubbed salt in the wounds late on turning in a rebound after Foster made an excellent save to deny Mane.
Key Talking Point
It's been mostly excellent or dreadful for Watford this season with little room in between, this was a performance much closer to the former. The team knew they couldn't match Liverpool across the pitch but didn't set up just to park the bus either.
Instead, opting to play on Liverpool's frailties, forcing mistakes at the back and attempting to hit them on the counter. Providing a constant threat throughout made it impossible for Liverpool to fully commit players forwards, with the Hornets backline looking resolute enough to withstand the pressure.
It put all the onus on Liverpool as the bigger side to enforce themselves on the game without making themselves too vulnerable at the back. They were always the second side in this game though and the ascendency told true in the end with Liverpool completing the victory.
Starting XI: Foster (8), Fermenia (8), Marriappa (7), Cathcart (8), Masina (6), Doucoure (6), Capoue (6), Hughes (6), Pereyra (8), Deulofeu (8), Deeney (7)
Substitutes: Success (6), Gray (6)
STAR MAN - Foster made a number of top-drawer saves but it's only a fraction of what he would have been facing without the excellent shielding of Craig Cathcart. Adopting such a bold approach to the game meant the defence had to be on point to prevent a shutout and Cathcart was excellent, keeping both Salah and Firmino quiet for large spells of the game.
WORST PLAYER - Gracia didn't make too many mistakes today but one key one was replacing Gerard Deulofeu with Isaac Success. The Spaniard had been a huge part of Watford's constant threat that halted Liverpool's progress playing in a forward role.
As the game drew on the manager looked to capitalise on their chances by putting an out-and-out striker upfront with a burst of pace but Watford never looked as dangerous once Deulofeu was removed. Success really struggled to offer a good attacking outlet for his side which allowed the Reds to take control of the game in the second half.
Key Talking Point
Liverpool have enjoyed a great start to the season regardless, but more questions will be asked as to if they can maintain Manchester City's blistering pace with performances like this. It was an excellent game plan from Javi Gracia to upset Liverpool but from Jurgen Klopp's perspective, it worked too well.
It was a distinctly average performance by Liverpool's standards, not quite managing to turn the screw and press home their ascendency. It wasn't the most convincing opener either but at least the Reds did hit their stride after finding the breakthrough and coasted to victory in the end. They continue to get the job done but it didn't look convincing for large periods today and that needs to improve if they hope to match Pep Guardiola's relentless champions.
Starting XI: Alisson (8), Robertson (5), Van Dijk (6), Lovren (5), Alexander-Arnold (8), Wijnaldum (5), Henderson (4), Mane (7), Firmino (6), Shaqiri (7), Salah (8)
Substitutes: Milner (6), Fabinho (6), Matip (6)
STAR MAN - It was a game of few heroes for the Reds despite the flattering scoreline, Klopp will demand more of his players going forward. The moment of the match goes to Trent Alexander Arnold for a spectacular free-kick to wrap up the points for his side.
WORST PLAYER - Jordan Henderson really let his side down today; a shame for the usually composed central midfield player. Having struggled to impose themselves on the scoreline throughout the first hour Liverpool were finally on top and cruising to victory with two goals inside 10 minutes.
Henderson then got involved in a couple of situations with Success that led to an early dismissal for him and rightly so for a reckless challenge. A couple of needless bookings with his team in control and Watford had shown enough to put pressure back on his side in the closing minutes, fortunately for him, they saw it out.
Watford face a tough trip to Leicester next before defending champions Manchester City visit Vicarage Road.
Liverpool meanwhile face a crucial Champions League clash against PSG before a Merseyside derby with Everton next weekend.