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.
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.
"I believe the lads deserved this win, regardless of whether the penalty should have been given or not," Milan coach Massimiliano Allegri said. "Having seen replays it looks like it wasn't a penalty. We have to always play with this intensity, even against the bottom team. ... Everyone said before the Napoli game that we were a dead team and instead we've had a great week."
It was only Juve's second loss in 53 league games. Inter Milan can now close the gap to one point if it beats Parma on Monday.
"We didn't play as a squad tonight, we couldn't manage to play our usual football," Juventus assistant coach Angelo Alessio said. "When you lose a game like this you always look for problems but it's just that the team didn't play as it has done in the past three or four games.
"We know that there are always mistakes for and against us. I don't dare to think what would have happened if we had won with such a penalty. It should have ended as a draw. But everything went against us tonight and we have to accept the defeat."
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.
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.
Milan President Silvio Berlusconi had made another visit to the training ground on Saturday to give the squad a pep talk and just like last week it had an immediate effect.
After his visit to Milanello last week, Milan came back from two goals down to draw 2-2 at title-chasing Napoli. It went on in midweek to secure qualification for the Champions League knockout stage.
Berlusconi was in the stands watching along with former Milan icon Marco Van Basten.
The Rossoneri almost got off to a perfect start as Mattia De Sciglio skipped past first Kwadwo Asamoah and then Andrea Pirlo before unleashing a shot from just outside the area which whistled past the left upright.
Milan had another good chance in the 14th minute but Kevin-Prince Boateng fired straight at Juventus goalkeeper Gianluigi Buffon following some good interplay with Robinho.
The Milan defence has been shambolic at times this season but it was dealing well with everything Juventus was throwing at it and stand-in goalkeeper Marco Amelia didn't have to make a save until the 21st minute when he gathered a weak shot from Fabio Quagliarella at the edge of the area.
Milan's penalty came on the half hour mark when Robinho crossed in towards Antonio Nocerino and the ball seemed to strike Isla on the side, but he was penalized for a handball.
Buffon guessed the right way and got a hand to Robinho's spot kick but couldn't prevent it from going in at the bottom left corner.
Juventus had its best chances of the game just after the hour mark. Amelia did well to punch Arturo Vidal's cross clear but it fell to Pirlo who put it back into the area, only for Mirko Vucinic to blaze woefully over.
The visitors went even closer moments later when Simone Padoin — who had come on as a halftime substitute for Isla — crossed in and Giovinco's acrobatic overhead kick flew narrowly wide.
In Pescara, Mattia Destro gave Roma the lead in the fifth minute and could have added to his tally but missed several clear chances.
It was the 100th official game in charge of Roma for Zeman, who is in his second spell at the club.
Elsewhere, Fiorentina's run of five successive victories ended after twice coming from behind to draw 2-2 at Torino.
Alessio Cerci, who is on loan from Fiorentina, gave Torino the lead in the 40th minute.
Gonzalo Rodriguez levelled from the spot but Torino restored its lead moments later when Valter Birsa's cross evaded everyone and ended up in the back of the net.
Fiorentina snatched a point six minutes from time when Mounir El Hamdaoui, who had only been on the pitch for less than two minutes, smashed home the equalizer.
Genoa is out of the relegation zone after ending a run of six successive defeats with a 1-0 win at Atalanta.
Andrea Bertolacci scored the only goal of the game in the 39th minute to hand Genoa its first win in 10 matches.
Genoa's Emiliano Moretti was sent off for a second yellow card four minutes from time.
Bologna lost 1-0 at Sampdoria after playing almost the entire match in 10 men following Archimede Morleo's dismissal. Andrea Poli grabbed the only goal of the game in the 61st.
Elsewhere, Siena drew 0-0 at Chievo Verona. Substitute Chievo striker Mamadou Samassa was sent off five minutes from time following a second booking.