Juventus started the season looking to win a 10th straight Serie A title but instead find themselves in danger of missing out on a Champions League spot after a 3-0 home defeat by top-four rivals AC Milan on Sunday left them fifth with three games left.
Goals from Brahim Diaz, Ante Rebic and Fikayo Tomori secured the win and sent Milan up to third on 72 points from 35 matches, leaving Juve a point behind fourth-placed Napoli and needing teams to drop points as they battle for a top-four finish.
Brahim curled home a stunning opener just before the break to give the visitors the halftime lead and they had a chance to extend the advantage in the 56th minute only for Franck Kessie's penalty to be saved by Wojciech Szczesny.
That miss did not prove costly, however, as substitute Rebic arrowed a fine strike into the net 12 minutes from time before defender Tomori, on loan from Chelsea, headed a third goal to seal a crucial win for Milan four minutes later.
Used to battling it out for the Scudetto in the past, Juve and Milan looked like two teams who were unsure of a top-four finish in a nervous first half.
Brahim lit up a poor first half after Szczesny did not get enough on a punch, with the Real Madrid loanee finding the top corner on his first start for Milan since March.
After the break, Juve did improve, with Ronaldo finally getting a shot away, but he could not find the target with his left foot, while Milan had to withdraw their top goalscorer this season, Zlatan Ibrahimovic, due to an injury.
Chiellini's clumsy handball gifted Milan the chance to extend their lead, after a lengthy VAR review. However, Szczesny came to the rescue - the Pole's third penalty save from the last four spot kicks he has faced in Serie A against Milan.
It was Ibrahimovic's replacement Rebic who effectively ended Juve's hopes of getting something from the match, before Tomori picked an opportune moment to score his first goal for Milan.
The final whistle was greeted with wild scenes of celebration from Milan staff and players, with their first away league win at Juve since March 2011 putting them in a strong position to return to the Champions League, potentially at their opponent's expense.