While second-placed West Brom came from behind to salvage a 2-2 draw at Derby, the Magpies made it six wins in a row as they saw off the Hornets.
And with the previously third-placed Leicester thrashed 5-1 at Nottingham Forest, it was almost perfect day for Chris Hughton's high-flyers in search of a quick return to the top-flight.
And this latest win was achieved after leading scorer Kevin Nolan was dismissed four minutes into the second half following two bookings.
A first-half strike from Peter Lovenkrands got Newcastle underway and then it was left to new signing Fabrice Pancrate to make it safe eight minutes from time after replacing Danny Guthrie.
At times it was hard going against a workmanlike Watford side that saw the deadlock broken after 20 minutes when Lovenkrands netted for the second game in a row at St. James' Park.
After scoring with a first-half header last time out against Swansea, the great Dane this time fired in from the edge of the area to give Scott Loach no chance.
Watford saw plenty of the ball and caused a number of problems without lacking the necessary finish.
Steve Harper returned in goal for United after missing the second half against Swansea with a back injury.
And United's longest serving player was twice called into action late in the first half to keep out Heidar Helguson efforts on each occasion.
United were then forced to play all but four minutes of the second half with just ten players.
Nolan, already booked in the first half, was cautioned again for a foul on Henri Lansbury and sent off.
United continued to play the ball about well and were rewarded when Frenchman Pancrate made the result safe after 82 minutes.
Involved for the second time as substitute, Pancrate rifled the ball high into the net from just inside the box.