AC Milan earned a surprising 1-0 victory over defending champion and Serie A leader Juventus on Sunday after another disputed goal at the San Siro.
Robinho scored his first goal of the season from the penalty spot, after Mauricio Isla was adjudged to have handled the ball in the area, although replays showed it appeared to have struck his side.
Fiorentina, meanwhile, rallied for a 2-2 draw against Torino and moved into a tie for second place in Serie A with Inter Milan, four points behind Juventus.
Sebastian Giovinco went closest to equalizing for Juventus but Milan always looked dangerous on the counter and had several chances to extend its lead as it recorded a morale-boosting win.
It was only Juve's second loss in 53 games.
Milan fans may feel it goes some way to atoning for a refereeing error in last season's match, which ended 1-1 after Sulley Muntari's goal was not spotted by the officials.
That match was a title showdown nine months ago, but few expected anything other than a Juventus win this time around, with Milan lying a dismal 12th and having lost six games already this season.
Fiorentina saw a run of five successive victories ended as it twice came from behind to draw in a pulsating encounter at the Stadio Olimpico.
Alessio Cerci put the home side in front in the 40th minute and Gonzalo Rodriguez responded from the penalty spot in the 74th minute.
Elsewhere, Roma won 1-0 at struggling Pescara to mark a happy return for coach Zdenek Zeman to the club he steered to promotion as Serie B winners last season.
Mattia Destro gave Roma the lead in the fifth minute and could have added to his tally but missed several clear chances.
Pescara went close to the equalizer in the closing stages but remains mired in the relegation zone after winning only one of its past eight games.
It was the 100th official game in charge of Roma for Zeman, who is in his second spell at the club.
Information from Press Association and The Associated Press was used in this report.