After a goalless first half which saw Newcastle waste several good chances, Cambridge took the lead through Joe Ironside. The Magpies failed to clear the danger after Martin Dubravka dropped the ball and the visitors took advantage.
Newcastle tried to find an equaliser but Cambridge were able to see the game out and book their place in the fourth round.
Eddie Howe named a strong side to face the League One outfit with new signing Kieran Trippier thrust straight into the starting line-up having only been confirmed as a Newcastle player the day prior.
But it was a frustrating start for the England international and his teammates as they were knocked out by a side ranked two divisions lower.
Here are Dominic Scurr’s player ratings from the match…
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1. Cambridge United's Bulgarian goalkeeper Dimitar Mitov makes a save during the English FA Cup third round football match between Newcastle United and Cambridge United at St James' Park in Newcastle-upon-Tyne, north east England on January 8, 2022. - - RESTRICTED TO EDITORIAL USE. No use with unauthorized audio, video, data, fixture lists, club/league logos or 'live' services. Online in-match use limited to 120 images. An additional 40 images may be used in extra time. No video emulation. Social media in-match use limited to 120 images. An additional 40 images may be used in extra time. No use in betting publications, games or single club/league/player publications. (Photo by Paul ELLIS / AFP) / RESTRICTED TO EDITORIAL USE. No use with unauthorized audio, video, data, fixture lists, club/league logos or 'live' services. Online in-match use limited to 120 images. An additional 40 images may be used in extra time. No video emulation. Social media in-match use limited to 120 images. An additional 40 images may be used in extra time. No use in betting publications, games or single club/league/player publications. / RESTRICTED TO EDITORIAL USE. No use with unauthorized audio, video, data, fixture lists, club/league logos or 'live' services. Online in-match use limited to 120 images. An additional 40 images may be used in extra time. No video emulation. Social media in-match use limited to 120 images. An additional 40 images may be used in extra time. No use in betting publications, games or single club/league/player publications. (Photo by PAUL ELLIS/AFP via Getty Images)
Cambridge United's Bulgarian goalkeeper Dimitar Mitov makes a save during the English FA Cup third round football match between Newcastle United and Cambridge United at St James' Park in Newcastle-upon-Tyne, north east England on January 8, 2022. (Photo by PAUL ELLIS/AFP via Getty Images) Photo: PAUL ELLIS
2. Martin Dubravka - 4
Made a couple of simple saves and claims but should have done better for Cambridge's goal as he spilled the ball. Photo: Shaun Botterill
3. Kieran Trippier - 6
Got involved early on and put some teasing balls into the box. Kept things simple and was an outlet down the right. Photo: PAUL ELLIS
4. Emil Krafth - 5
Was steady in a central defensive role but had little to do. Photo: Richard Heathcote