Sampdoria made a winning return to Serie A with a shock victory at AC Milan, whose new-look side failed to ease their fans' pre-season concerns.
Andrea Costa scored the only goal of the game in the 58th minute and, although the Rossoneri hit the woodwork twice, their fans made their feelings clear at the final whistle.
Milan coach Massimiliano Allegri will now have more questions to answer after shedding several key players this summer while Samp showed that they can be competitive in the top flight after spending one season in Serie B.
It was Milan's first outing since the sale of Zlatan Ibrahimovic and Thiago Silva to Paris St-Germain while new signing Giampaolo Pazzini, who traded Milan clubs with Antonio Cassano, started on the bench.
It appeared many Milan fans had voted with their feet, leaving the San Siro only half full with the crowd swelled by a sizeable travelling support as Samp fans flocked to witness their return to the big league.
There was not much to write home about for the fans, though, during a dismal first 45 minutes.
The only chance was wasted by Samp striker Eder, but Daniele Bonera made up for his mistake in letting the forward get away by recovering ground to get in a tackle.
Samp went ahead in the 58th minute was Costa sent an unstoppable header past Christian Abbiati following a corner.
Mario Yepes replied at the other end six minutes later, but his header was pushed onto the post by Sampdoria goalkeeper Sergio Romero, who collected the rebound.
Pazzini soon took to the field but Milan struggled to find a way through as Sampdoria defended in numbers.
The home team almost grabbed an equaliser in stoppage time when they hit the woodwork again, this time Kevin-Prince Boateng frustrated as the ball stayed out.
And Mathieu Flamini wasted the last chance of the game as Daniele Gastaldello cleared his effort off the goal line.