After a tough first 20 minutes of their opening US tour match, Chelsea took the lead thanks to a expertly-taken Loic Remy strike, and looked comfortable heading into the break.
However, some woeful second-half defending saw the under-strength hosts turn the game right around with Franklin Castellanos, a Sean Davis double and Tyler Adams sending the home fans into a state of shock.
Eden Hazard’s fine goal was mere consolation as the Blues rearguard gave Jose Mourinho plenty of dilemmas ahead of Saturday’s International Champions Cup clash with Paris Saint-Germain.
Chelsea faced a much-changed Red Bulls side who had played a competitive match just 30 hours previously, but with the MLS outfit well into their domestic season, they were much sharper than their illustrious opponents, who didn’t have Radamel Falcao available, despite him taking part in the warm-up.
However, it was the Premier League champions who showed the necessary quality in front of goal, with Victor Moses testing New York goalkeeper Kyle Reynish after a fine run.
Remy broke the deadlock on 27 minutes, despite appearing to be in an offside position. Oscar looked like he had delayed the cross too long, but he picked out the French hitman, the flag stayed down, and after dummying delightfully, he slotted home with aplomb.
Moses again almost got on the scoresheet from a tight angle, but his dinked finish came back off the post with Reynish beaten.
After the break Chelsea made a raft of changes, but with Diego Costa, Eden Hazard, John Terry and Nemanja Matic entering the fray it looked ominous for the hosts.
However, just after brilliantly getting back to cover for an error from fellow substitute Asmir Begovic and clear off the line, John Terry’s poor backpass was seized upon by Castellanos, who beat Begovic to the ball to equalise on 51 minutes.
Costa was proving to be a real menace, but his ruthlessness in front of goal had deserted him, as he blazed over the bar after his own header had come back off the crossbar just after the hour mark.
It got worse for the Blues on 69 minutes as Cesar Azpilicueta did not get close enough to cut out a cross, which picked out Tyler Adams, unmarked, and he glanced a header past the despairing dive of Begovic to put his side in front for the first time.
More poor defending saw the Blues fall further behind just two minutes later as Davis grabbed his first of the evening after another cross was not cleared properly.
Hazard immediately got the champions back into the encounter, firing into the bottom corner after collecting a well-worked free-kick on the edge of the box, but it was to no avail as chaos still reigned down the other end.
This time Ramires was the guilty party, as he failed to clear yet another cross, instead scuffing into the path of Davis who rifled home, via a deflection.
Costa again missed a gilt-edged chance, while Oscar elected to side-foot an effort at goal from a good position, but he failed to connect properly and the ball rolled harmlessly wide.
The MLS franchise held on for an impressive result considering the personnel they had available, but Mourinho will not be pleased that the normally resolute Blues were undone so easily.