Juventus coach Massimiliano Allegri slammed referees after seeing Miralem Pjanic's goal chalked off as the champions were stunned 1-0 by AC Milan in a San Siro sizzler Saturday.

The Turin giants had beaten Milan in the sides' last nine meetings and, in front of 75,829 spectators, showed throughout a stirring encounter why they are being tipped to claim a record sixth consecutive 'scudetto' title at the end of the season.

But Juve's failure to find a way past Milan's teenaged goalkeeping sensation Gianluigi Donnarumma proved costly, and the visitors were given few favours by referee Nicola Rizzoli on their way to a second successive San Siro setback just over a month after suffering a 2-1 reverse to Inter Milan.

Pjanic looked to have finally broken the deadlock for the visitors when he spun away in delight to celebrate beating 17-year-old Donnarumma with a rasping free kick just after the half-hour.

But the Bosnia midfielder's joy was short-lived. Milan's players surrounded Rizzoli claiming offside and after consultation with his touchline official he cancelled the goal.

Allegri said: "It's clear our goal was valid. I shouldn't say it, but everyone will say it."

He suggested Milan's protests had influenced the officials' decision.

"The first protests from Milan certainly put the pressure on, but we should focus on playing: anyway, this result shouldn't alter the path we're on. People say we played badly, but I feel that, tonight, we played well technically, and lost.

"I can't find fault with the lads, they controlled the game and created shots and goalscoring chances. We shouldn't worry about this result."

Juve remain top but their second loss of the league campaign has added a new, dramatic twist to this season's fight for the Serie A title.

Milan moved up to second to sit only two points adrift to signal their return to the fray after several seasons struggling to keep pace and falling down the pecking order in Europe.

The defeat also brought Juve within reach of Roma, runners-up in 2014 and 2015 and who could reclaim second place from Milan, and sit two points behind, if they account for Palermo on Sunday.