A week after being booed off the field for a humiliating performance against Aston Villa, Middlesbrough shook the reigning champions with a superb display.
Middlesbrough fans looked on in astonishment, and obvious jubilation, as their team recorded only a second Premiership defeat of the season on Chelsea.
The Londoners could have no complaints about the result. They piled on fierce pressure to try and pull the game round but Boro defended with resilience and looked dangerous on the counter-attack.
Middlesbrough have an astonishing record at the Riverside Stadium this season. They have beaten Chelsea, Manchester United and Arsenal - yet lost to bottom of the table Sunderland!
"Why can't we play the top teams every week?" asked a bewildered Middlesbrough fan near to the press box at the final whistle.
Boro boss Steve McClaren must have been mightily relieved with the result and the performance.
McClaren has been under severe pressure with his side slipping towards the relegation zone.
He had insisted all along that there was a good dressing room spirit and certainly his players responded to his rallying call.
Chelsea manager Jose Mourinho, however, must have been bitterly disappointed with the performance of his team. There was not one outstanding player in his side.
Jubilant Middlesbrough fans rubbed it in by chanting "are you Sunderland in disguise?" during the second half.
After the doom and gloom of recent weeks no-one could begrudge Middlesbrough fans enjoying the occasion, and the result should certainly boost their prospects of avoiding the drop at the end of the season.
The hosts got off to the best possible start with a goal after 80 seconds.
Former Sporting Lisbon and Barcelona midfielder Fabio Rochemback celebrated his first Middlesbrough goal but Chelsea goalkeeper Petr Cech must have been disappointed with his attempt at a save.
Shortly afterwards Cech denied a second Boro goal with a brilliant save from a powerful Stewart Downing shot.
Middlesbrough midfielder George Boateng made a long awaited comeback when he took over from the injured James Morrison after 39 minutes.
In first-half injury-time local hero Downing sent the crowd into raptures when he cut into the penalty area and shot into the net.
Chelsea, not surprisingly, piled on fierce pressure in a bid to save the game.
There was a cup-tie atmosphere, with Middlesbrough fighting tooth and nail to keep out the champions.
Despite the pressure, home goalkeeper Mark Schwarzer was rarely tested.
Middlesbrough were more dangerous in quick counter-attacks and made certain there was no coming back for Chelsea when Yakubu put them further ahead after 68 minutes.
The Nigerian beat Chelsea skipper John Terry to place the ball past Cech for his 16th goal of the season.
In the closing stages Chelsea substitute Carlton Cole struck the woodwork, while at the other end Cech made a superb save when he tipped round the post a brilliant Rochemback shot.
The result will surely put Middlesbrough in good heart for the crucial six-pointer at West Brom next Sunday.