The relegation-threatened club was held to a 1-1 draw by Watford, who claimed a point through a late Joao Pedro equaliser.
A win would have lifted Newcastle out of the relegation zone for the first time since the start of October, and a Allan Saint-Maximin put them ahead after the break with a superb solo goal.
That was to be the club’s only shot on target. United sat back after going in front, and there was an inevitability about their equaliser.
Elsewhere, Norwich City beat Eveton 2-1 to climb above United, who have taken just 12 points from 20 games this season.
Eddie Howe, as expected, handed striker Chris Wood, signed from Burnley for £25million this week, his full debut. What was less expected was the start handed to Paul Dummett, who hadn’t played a minute of Premier League football since May 23 last year due to a calf injury.
Newcastle, set up in a 4-3-3 formation, tried to apply some early pressure on their visitors, and Joelinton struck the crossbar early in the game from a deflected cross.
United, however, couldn’t get the ball to Wood in the box, and Watford, with ex-Newcastle midfielder Moussa Sissoko in midfield, came back at them. There were a few first-half scares for Howe’s side, despite their dominance, and Claudio Ranieri’s side, pressing high up the pitch, made life difficult.
That said, United pressed on themselves. Joelinton, arguably Newcastle’s best player, put another chance wide, while Wood headed over from a corner.
Wood was crying out for decent deliveries into the box, but those were few and far between. Saint-Maximin, playing on the left, struggled to play a telling final ball during a scrappy and niggly first 45 minutes.
What the game needed was a moment of quality, and Saint-Maximin provided it in the 49th minute.
Saint-Maximin won the ball on the left and battled into the box before beating Ben Foster with a low, right-footed shot which lifted the roof at a sold-out St James’s Park.
United had dropped 19 points from winning positions in their previous 19 Premier League games – and the challenge was to hold on to that lead.
Newcastle found themselves on the back foot with 20 minutes left. Howe sent on Jacob Murphy and Miguel Almiron, but his team lost the initiative.
Matt Ritchie, warming up on the sidelines, joined the club’s fans in urging the team on for the final 10 minutes.
United couldn’t hold on much longer. Pedro got between Jamaal Lascelles and Kieran Trippier to head a Kiko Femenia cross home in the 87th minute and – and keep Newcastle in the bottom three.
Howe looked on in disbelief as Watford celebrated – he couldn’t believe what he had seen.
The 43-year-old, pained by the equaliser, joined his players on the pitch to applaud the club’s frustrated fans after the final whistle.
The club’s head coach and his squad can only hope that they’ll get another chance to climb out of the relegation zone.
NEWCASTLE UNITED: Dubravka, Trippier, Lascelles, Schar, Dummett, Shelvey, S Longstaff, Joelinton, Fraser (Murphy, 74), Saint-Maximin (Almiron, 85), Wood. Subs not used: Darlow, Gillespie, Ritchie, Lewis, Krafth, Willock, Anderson.