Steve McClaren selected £12m striker Aleksandar Mitrovic in his Newcastle line-up at York and saw the recent arrival twice go close to a goal.
But it was League Two York who came away with a win as Anthony Straker’s fortunate opener and a second, more impressive, strike from a trialist gave them a 2-0 lead.
Ayoze Perez scrambled a late goal for the visitors on his 22nd birthday, but that was as good as it got.
While Newcastle were slipping to defeat at York, Sunderland were coming a cropper at the Keepmoat, where Doncaster won 2-0 thanks to goals from Cedric Evina and Harry Forrester.
One plus point for Dick Advocaat was a lively performance from Jeremain Lens, the Holland midfielder signed from Dynamo Kiev this summer.
Lens had several decent efforts on goal, and there was also a second-half debut for centre-half Younes Kaboul.
Leicester were the third Premier League side in action and had better luck than their peers, fine goals from Riyad Mahrez and David Nugent giving them a 2-1 at Rotherham.
Elsewhere, Derby drew 1-1 with Villarreal and there were two goals each for Kike and Albert Adomah in Middlesbrough’s win at Barnsley.