He teed up three of the efforts recorded by Jurgen Klopp’s side at Anfield, with Sadio Mane benefitting on two occasions from the find work of a team-mate before Virgil van Dijk nodded home a cross late on.
Alexander-Arnold has become the youngest player to register three assists in a Premier League fixture, with the 20-year-old admitting that his success was down to exploiting a weakness identified in Watford’s game prior to kick off.
He told Liverpool’s official website: “Obviously it’s every full-back’s dream to provide assists and to get three in a game is probably not something I’ll get the privilege of saying too often.
“But I’m happy to be able to provide the team with chances to score and credit to the lads for taking them, especially Virg with his two goals, who’s shown that he’s a real aerial threat.
"It was one of them where maybe their wingers weren’t probably that enthusiastic in tracking us and if the lads got the ball out wide to me and Robbo, that maybe we could provide crosses in and that’s the way it worked.
"I think especially first half we had a lot of freedom down the sides and we tried to provide as many balls into the box as we could for the lads.
"We had a bit more of an aerial threat with Sadio being so good in the air and Divock [Origi] coming into the team, who’s a big lad, so it was important for us to give them service and that’s what we did."
A crushing victory on home soil has helped to keep Liverpool at the top of the Premier League table – one point clear of defending champions Manchester City.
The Reds had faced accusations of showing nerves in the battle to land a first crown in 29 years, but Alexander-Arnold claims those at Anfield are revelling in a bid to restore domestic dominance.
He added: “I think the main thing for us going into the game was to enjoy it and I think it’s not very often where players are in this position that they’re fighting for a league title, so a lot of the lads it’s our first time of doing it so we all just want to enjoy.
“We want to embrace it as much as we can, go with the flow and hopefully pick up results when we can and that’s what we tried to do today: just enjoy it, go out there and play fluid.
“That was the main thing for us, to get back into a rhythm and that’s what we did. It looked really good and it felt really good to be out there.
“We know that it is one game at a time, but right now we are top of the league. It’s something to be proud of - not many players can say that they are at this point of the season.
“There’s 10 games left now so I think the fans know we need as much support as possible and hopefully we can put in performances like this and we can give back to them by bringing results and performances like today.”