Slaven Bilic saw Declan Rice and then substitute Manuel Lanzini caught in possession for the first and second goals.
The Croatian has been under the spotlight in recent weeks and a third successive defeat, all of them away from home as a result of of the World Athletics Championships being held at the London Stadium, will do little to quell the speculation.
Bilic said: "Look, I am the manager, it's my job to be confident and to believe in good and bad times. Even when the times are bad, then you see the importance of the job more than in the good times. I haven't changed in that.
"They [Newcastle] were better in every aspect of the game. They had simply more power, more determination."
Bilic admitted he was worried by his side's performance on Tyneside and challenged his players to dig themselves out of the hole into which they have slipped.
He said: "I am worried. I'm not panicking, but...
"It's very early, but after the game against Southampton, we lost the game, we still had zero points but I was still very, very positive with the way we played, with the way we reacted after we were left with 10 men.
"This is different, this is worrying, but like for every club, it has its ups and downs and nobody will take us out of this situation but ourselves."