Newcastle harbours huge ambitions after it was taken over by a Saudi-led consortium in October and was eyeing a long-awaited cup run under recently-appointed boss Eddie Howe.
But the Magpies were beaten 1-0 in the third round by Cambridge, which was on a three-game winless run and is 16th in League One, through Joe Ironside's 56th-minute strike from close range at St James' Park.
🗡 𝗦𝗶𝗿 @22Mitov has a ring to it 🗡— Emirates FA Cup (@EmiratesFACup) January 8, 2022
A heroic defensive performance a long with a Joe Ironside goal sends @CambridgeUtdFC through to the #EmiratesFACup fourth round after overcoming Newcastle United! 🙌#EmiratesFACup pic.twitter.com/u2gKYAVG55
The victory was Cambridge's first playing away at a top-flight side in the FA Cup and means the U's have now won as many games against Premier League opposition this season as Newcastle has in 19 matches.
While Newcastle has yet to truly flex its financial muscles, it brought in Kieran Trippier from Atletico Madrid for £12 million ($22. 5 million) this week and the full-back played a full part in front of United's hugely wealthy owners.
Cambridge goalkeeper Dimitar Mitov made nine saves in total, including a sensational stop to deny Joelinton late on, as Mark Bonner's side made it through to the fourth round for only the second time in 21 seasons.
Second-bottom Newcastle must now turn its attention back to the battle to stay in the Premier League, with a huge clash against fellow-struggler Watford to come next weekend.