Mario Yepes and Kevin-Prince Boateng both struck the woodwork late on for the Rossoneri but they deserved nothing out of a game in which they were far from their best
The Rossoneri had more of the ball during a tepid first-half, but they did so very little with it that the visitors could not help but grow in confidence the longer the game wore on.
As a result it came as no surprise when the Blucerchiati took the lead on 59 minutes when Andrea Costa headed the newly-promoted outfit into the lead.
Milan tried to rally in the final half an hour, but while Mario Yepes and Kevin-Prince Boateng struck the woodwork late on, Massimiliano Allegri's men slumped to a disappointing yet thoroughly deserved defeat after a horribly uninspiring performance.
The rows of empty seats at the Giuseppe Meazza underlined just how disillusioned and demoralised Rossoneri fans feel after a summer sale that saw their once mighty club forced to offload their two best players, Thiago Silva and Zlatan Ibrahimovic, to Paris Saint-Germain in order to balance the books.
Those supporters that did bother to show up must have been feeling like they should have stayed at home, after a stale first-half in which a Milan side devoid of almost any creativity and dynamism in the middle of the park managed just one shot on target - and even that was an effort from Robinho which flew straight into the arms of Sergio Romero.
Indeed, despite playing just one striker, Sampdoria carried the greater attacking threat in the opening 45 minutes and went closest to breaking the deadlock.
Daniele Bonera appeared to have things under control when Marcelo Estigarribia aimed a diagonal ball in the direction of lone forward Eder.
However, the dozing Milan centre-half allowed himself to be dispossessed by the Blucerchiati striker, who then proceeded to cut inside towards the Milan goal. Eder, though, took too much out of the ball and allowed a relieved Bonera to get back to block the Brazilian’s goal-bound effort.
The home side looked ever so slightly more menacing at the start of the second-half, with Robinho having two cracks on goal, albeit to no avail, while Giampaolo Pazzini’s entry into the fray in place of the ineffective Stephan El Shaarawy did give the Milan fans something to sing about.
However, they were silenced just moments later when left-back Costa climbed highest to power home a corner from the right-hand side.
Milan very nearly equalised in almost identical fashion on 64 minutes, but Romero managed to parry Mario Yepes’ towering header onto the post before the ball bounced back into the grateful arms of the keeper.
The Rossoneri continued to press and Boateng was unlucky to see his curling effort from outside the area strike the right post, while Mathieu Flamini was denied at point-blank range.
But the visitors survived to announce their return to Serie A with a win that was greeted with a sense of bewilderment by the home fans, who may be envisaging a long season ahead.