MILAN (Reuters) - A stunning second-half strike by 18-year-old Manuel Locatelli gave AC Milan a 1-0 win over Juventus after the Serie A titleholders had a goal controversially disallowed on Saturday.
Juventus thought they had gone ahead in the first half from Miralem Pjanic's free kick but the goal was ruled out for offside after a two-minute consultation between match officials.
It was Milan's first win over Juventus for nearly four years and ended a run of nine successive defeats against the Turin side.
Earlier, an unlucky own goal by Armando Izzo handed Sampdoria a 2-1 win over neighbours and bitter rivals Genoa in a pulsating derby. Sampdoria also missed a penalty in first-half stoppage time.
Juventus stayed top with 21 points from nine games but Milan closed the gap to two points.
Juventus have won the last five Serie A titles while Milan have slumped into midtable mediocrity but the seven-times European champions have made a bright start this season under new coach Vincenzo Montella.
The game at San Siro was an intense, tactical battle but erupted in controversy after 35 minutes.
Pjanic floated a 35-metre free kick over the wall, Juve's Leonardo Bonucci lunged and failed to make contact with the ball but distracted Milan goalkeeper Gianluigi Donnarumma and it flew into the net.
Juventus players were back on the halfway line waiting for the restart when referee Nicola Rizzoli disallowed the goal for offisde against Bonucci although replays suggested he was onside when the ball was played.
Locatelli added to Juve's sense of injustice when he collected Suso's pass and fired an unstoppable shot past Gianluigi Buffon into the top corner in the 65th minute.
Donnarumma, 17, ensured Milan's win by turning away Sami Khedira's long-range shot with the last kick of the game.
Sampdoria ended a six-match winless run that had put coach Marco Giampaolo's job on the line in the so-called Derby of the Lighthouse.
Genoa's misfortune came two minutes into the second half when Luis Muriel crossed from the right, goalkeeper Mattia Perin palmed the ball away but it flew straight at Izzo and rebounded into the net.
Colombia forward Muriel, a constant thorn in Genoa's side, gave Sampdoria the lead after 12 minutes when he side footed the ball home after Fabio Quagliarella cleverly laid the ball into his path.
Luca Rigoni levelled in the 24th minute from Edenilson's pass and the hapless Izzo saw a shot hit the crossbar shortly after that.
Quagliarella won a penalty for Sampdoria in first-half stoppage time and the same player took the spot kick but saw his effort saved by Perin.
Writing by Brian Homewood, editing by Pritha Sarkar