It was Newcastle who started the brightest, and they thought they had taken a very early lead when Mikel Merino met Matt Ritchie's corner on the edge of the box. His volley was, however, saved well by Matthew Ryan at his near post.
Brighton did come back into the game, in fact they looked the better side for the next twenty minutes. A Solly March delivery from the left caused havoc in the Newcastle penalty area, only for Chancel Mbemba to clear for his side.
The best chance of the game fell to Brighton's star creator Pascal Groß, but his volley struck his own teammate Anthony Knockaert and bounced wide of the post.
Joselu, who was guilty of missing a hat-rick of chances last weekend against Stoke, pulled a left-footed shot wide. That was the away side's best chance of the half. It should have been 1-0 to the Magpies.
Christian Atsu was lively in the opening 45 minutes and almost picked out Ayoze Perez in the box after his pull-back. The Spaniard was inches away from connecting with the ball.
It was almost a carbon copy minutes after that, only this time it was Mbemba who slid a ball across to Perez. This time Perez did meet the cross, but his shot sailed over the bar.
Jamaal Lascelles gave away a needless free-kick 35 yards out, which Newcastle ultimately paid the price for. Groß delivered it, Dale Stephens headed across and Tomer Hemed flicked the ball over Rob Elliot and into the roof of the net. 1-0 to the hosts.
Moments later, Rob Elliot was forced into a brilliant save to deny March after Lascelles had given the ball away. Newcastle were rocking at the back.
They did eventually ride out the Brighton storm, and began to create chances of their own. A deflected shot from Merino looked to be heading into the top corner, but it flew inches wide.
Jonjo Shelvey was introduced with twenty minutes to go and without a doubt, he provided an attacking influence that United simply didn't have without him.
From a corner on the left, the midfielder rattled the inside post. Newcastle inches away from an equaliser.
Mikel Merino slipped Shelvey through on the left, and just when Ciaran Clark looked ready to slot in the latter's cross, Lewis Dunk was there to block.
Half chances for Lascelles and Christian Atsu proved the best Newcastle had to offer in the dying embers of the game.
It is very much a case of being brought back down to earth for Rafa Benitez and his side. A poor performance and poor result, but not the end of the world by any means. Next up, Liverpool at St James' Park.