Watford took the game away from Newcastle within 28 minutes of the kick-off.
Daryl Janmaat gave the Magpies hope when he pulled one back with 28 minutes remaining - and he tested goalkeeper Heurelho Gomes with a 67th-minute piledriver.
It was the Magpies' first league goal in 464 minutes of football - but it was not enough to prevent them extending a desperate record of just one win in 17 outings dating back to last season.
Steve McClaren, who heard his side booed from the pitch at the end of both halves, said: "I can understand the fans' reaction.
"We are just turning things around and I think the majority understand that. Like we have said to the boys in the dressing room, it's not a crisis, it's not a time to panic - it's too early, and we'd never do that anyway.
"No matter where you are at what stage, we'd never do that, we have too much experience to know that.
"Like I've said to the players, we have got to stick together. We are going to get a lot of criticism and that can be flying from not just media, but also fans, and in that dressing room we have got to stay tight, we have got to stay calm, we have got to stick together.
"I am under no illusions, this is a hard job - everybody knew that and you know it. You want proof, we've got proof.
"But we have got the experience in the backroom staff to deal with this and turn it around. We are lucky that it's early - it's only two and a half months that we've been working with each other and there's a long way to go and a lot of things to do."