Put his side under unnecesssary pressure with a poor kick-out early on but Yepes came to his rescue. In truth, he did not have an awful lot to do thereafter - under than pick the ball out of the back of the net following an Andrea Costa header that he could do little about.
His willingness to get forward was evident right from the opening minute, with the left-back positioning himself inside Samp territory. However, one decent surge to the byline aside, he offered little by way of an attacking threat. Did not do too much wrong defensively, but he was caught out by a clever ball in behind him by Obiang which Estigarribia only just failed to collect.
M. De Sciglio
Defensively solid, but he only really came to life in an attacking sense after Milan had fallen behind. Difficult to be too harsh on him, though, when he was actually one of the hosts' better performers, putting over a number of inviting crosses late on.
A liability throughout, the defender was caught napping by Eder 10 minutes in, allowing himself to get dispossessed wide on the right-hand side. Though he made amends by getting back to block the striker's effort on goal, he presented the striker with another opportunity to run at goal later in the half.
Selected ahead of Zapata and justified his inclusion with a relatively commanding display - certainly in comparison to his central defensive colleague Bonera. The Colombian was commanding in the air and had already served notice of his threat at set-pieces in the opening 45 minutes before seeing Romero pull off a wonder save to keep out his second-half header.
By no means a poor performance, the Frenchman brought dynamism and energy to the game, but not enough. The former Arsenal man also squandered a decent opportunity to level matters when he snatched at a corner midway through the second half.
When he wasn't sitting too deep, he was stepping on Robinho's toes wide on the left-hand side. His passing was poor and he was uncharacteristically subdued. No surprise when he was hauled off 15 minutes before the end.
Tried to dictate things from the base of the Milan midfield, but he was caught in possession just outside his own box, with his mistake went unpunished by Obiang. Admittedly, the Italy international put himself about for his side.
He was one of the few players clad in red and black who showed some urgency and was always willing to run at the Sampdoria defence. Terribly unlucky not to snatch a point for his side with a terrific 25-yard effort that struck the right post. Just a frustrating afternoon for the trequartista.
S. El Shaarawy
Selected ahead of new signing Giampaolo Pazzini, he started encouragingly enough, but he was a peripheral figure for most of the first half. His most notable contribution after the break was a dreadful lay-off which ruined a promising Milan attack, and he was replaced by Pazzini moments later.
Positioned himself wide on the left for much of the first half and looked dangerous whenever he cut inside onto his right foot. Tried to lift Milan at the start of the second half, firing a couple of shots from distance in the direction of Romero, and his endeavour made the decision to replace him all the more surprising.
Depressingly from a Milan perspective, he was given almost nothing to do before Samp broke the deadlock. However, he pulled off a stunning save to deny Yepes shortly after Costa's opener, and also denied Boateng right at the death.
Was not quite as eye-catching as his central defensive partner, but he turned in a no-nonsense performance and deserves just as much credit for subduing the likes of El Shaarawy and Pazzini.
A wonderfully committed performance from the defender, who typified Sampdoria's spirit with a tremendously timed challenge on Robinho, just when it seemed that the Brazilian might beat him to the ball and put himself in on goal. He was later booked for hauling down the Milan forward but that did not detract from an influential display.
Look vulnerable on occasions, particularly when faced with Robinho's dancing feet, and his passing was a tad nervy, too. However, he played his part in a fine rearguard action from the visitors.
The new signing was a great outlet for Sampdoria down the left-hand side, even if his delivery was poor at times. Defended stoutly enough, though he was troubled by Boateng on occasion. Ultimately proved the match-winner, though, with a towering header.
Broke up play well and looked very composed in possession. Did not do anything spectacular but was effective and efficient throughout.
The winger, who spent last season with Juventus, looked lively whenever he got on the ball but his attacking instincts were curbed somewhat by the defensive responsibilities placed upon him. His shooting was wild but he ran himself into the ground before being taken off.
Offered little by way of an attacking threat but, just like Estigarribia, he was clearly asked to track back as much as possible in order to contain Milan's full-backs. Put in a decent shift in that regard.
Strong and imposing, he was not afraid to put his head in where it hurts - literally, the midfielder picking up a nasty head wound midway through the first half. Confident on the ball, he got forward at every opportunity and nearly scored after catching Montolivo in possession at one point.
A swift return to San Siro for the midfielder, who spent the second half of last season on loan to Inter. Did not quite see enough of the ball as he would have liked but was nice and tidy in possession.
Led the line superbly for Sampdoria, proving an absolute menace to the Milan defence, and Bonera in particular. Took too many touches after dispossessing the defender during the first half but he did not let the missed opportunity affect him and it was his solo run that led to the corner from which Samp scored. Looks like a great signing.
Thrown on in place of Robinho but was nowhere near as lively as the Brazilian.
Replaced Nocerino during the second period and showed plenty of energy and drive - without really making his presence felt.
Came on 10 minutes into the second half for the ineffective El Shaarawy but did not look like altering the course of the game.