Cabaye leaves United title defence hanging by a thread
The loss to Alan Pardew's side -- the first time Newcastle have won at Old Trafford since 1972 -- was the champions' fifth of the campaign and leaves manager David Moyes under increasing pressure to turn their season around.
After the 1-0 defeat by Everton in mid-week, Moyes insisted that his team could still close the 12-point gap to leaders Arsenal.
But while he will continue to put on a brave face in public, Moyes must be concerned by the lacklustre nature of his team's performances, as well as their poor results.
Robin van Persie returned from a month out with a groin problem, but was given little service from a midfield four that was completely changed from the Everton defeat.
Cabaye finished off a quick Newcastle break just after the hour, but the final half an hour was an alarming indication of United's problems, with visiting goalkeeper Tim Krul barely called into action.
The hosts' new-look midfield took time to settle, and when Adnan Januzaj opened up Newcastle's defence with a fine pass for Phil Jones, the England international could only shoot straight at Krul.
After a surging run down the left flank from Patrice Evra, Tom Cleverley had shots blocked by Fabricio Coloccini and Mike Williamson as the visitors struggled to clear.
Pardew's side threatened for the first time when Loic Remy glanced a header wide of goal from Moussa Sissoko's cross.
France midfielder Cabaye also dragged wide of David de Gea's goal after he was picked out by a pass from Cheick Tiote.
As the Old Trafford crowd grew frustrated with Moyes's side's lack of creativity, Newcastle broke quickly, with Sissoko slipping the ball inside for Cabaye, whose long-range effort looped up off Cleverley and dropped just over the bar.
Tiote also surged forward and had a shot over from distance, while the home side had a penalty appeal turned down when Hernandez went down theatrically in the area after Coloccini pulled out of a challenge.
Mathieu Debuchy also went close on two occasions just before the break.
The France right-back was found by Remy with a neat pass in behind the home defence, but was denied by a save from De Gea, who repelled a firm header from the same player moments later.
Moyes's side at least began the second period with greater intensity and began to work Krul.
Van Persie's raking pass picked out Hernandez and the Mexican's shot was saved by the Dutchman, who also made a scrambling stop from Januzaj.
Shortly afterwards, Evra met Van Persie's corner with a firm header that bounced off the post and appeared to hit Vurnon Anita's hand before being cleared.
Newcastle appeared to be struggling to cope, but after Sissoko thumped over the bar from distance, the visitors took the lead.
Sissoko beat Evra and burst into space down the right before pulling the ball back for Cabaye, who swept a shot into the bottom-left corner from the edge of the area via a deflection off Nemanja Vidic.
Moyes brought on Wilfried Zaha for his Premier League debut as the hosts looked for a way back, but Hatem Ben Arfa drove over from long range as the home side found it hard to get out of their own half.
United did put the ball in the net when Van Persie headed in from a Januzaj free-kick, but it was ruled out for offside.
Zaha also went close, curling just wide of Krul's goal from a position on the left, while Van Persie saw a bending free-kick fly just past the post, but Newcastle held on for a historic victory.