Accepting a square pass from Firmino, Salah jinked past a crowd of Watford defenders before putting Cathcart on his backside and cutting inside to curl past Foster.
It was the lowest of low key assists from Firmino but still showed his importance to the side.
He capped a brilliant afternoon by tapping in Neco Williams’ cross to complete his hat-trick in injury-time.
In the majority of games, Klopp has fielded Diogo Jota in between Mane and Salah this season. The Portuguese forward has looked the part, scoring three goals in nine games, but he is a completely different style of player.
Jota is a clever inside forward capable of drifting into space and timing his runs into the box. Firmino’s style has made him the lynchpin for Liverpool’s attack for the past three seasons: he holds up the ball, brings his team-mates into play and more often than not finds himself in the right place at the right time.