First-half goals from Luca Gagliano and Giovanni Simeone gave Cagliari a deserved 2-0 victory over Serie A champions Juventus.
Juve wrapped up their ninth consecutive title with a 2-0 win over Sampdoria at the weekend, although patchy recent form means Maurizio Sarri's side have now won only two of their past seven matches.
A vibrant Cagliari were the beneficiaries on this occasion, with Gagliano giving them an early lead to set them on the way to a first July win at the ninth and final attempt.
It proved a frustrating night for Cristiano Ronaldo, while Simeone – the son of Atletico Madrid boss Diego – came up with a superb finish worthy of the five-time Ballon d'Or winner in first-half stoppage time.
Gianluigi Buffon was back in the Juventus starting line-up and picking the ball out of his net in the eighth minute, when Federico Mattiello drove Paolo Farago's right-wing cross back across goal for Gagliano to finish from close range.
Ronaldo – engaged in what appears to be an increasingly futile pursuit of Ciro Immobile in the Capocannoniere stakes – touched in Federico Bernardeschi's stabbed through-ball from an offside position and racked up four blocked attempts by the interval.
Gonzalo Higuain volleyed over from Bernardeschi's 38th-minute corner before Juve found themselves further behind due to Simeone's sublime 20-yard drive.
Joao Pedro sent a shot from similar range skimming wide early in the second half before Buffon plunged to keep out a Simeone volley – the defence in front of the veteran gloveman continuing to look terribly disjointed.
Atalanta-bound Simone Muratore had a long-range effort saved by Cagliari keeper Alessio Cragno, who also got down sharply to keep out Ronaldo's left-footer from 25 yards in the 68th minute.
Simeone might have added to his tally and Juve's misery when he sliced wide before the visitors pounded at the Cagliari defence with diminishing return until the final whistle.
What does it mean? Sarri has steepening Champions League task
The more Juventus turn in performances like this, the less their schedule of competitive action before the second leg of their Champions League last-16 tie against Lyon feels like an advantage.
The Ligue 1 side have, of course, been out of action since March as they prepare to defend a 1-0 lead in Turin next month. Sarri badly needs his team to find some rhythm, something an experimental line-up entirely ruled out in Sardinia.
Simeone back in the groove
The moment of defining quality was produced by Simeone as he sized up a backpedalling Leonardo Bonucci before lashing beyond a helpless Buffon. It was his 12th goal of the Serie A season – closing on the 14 he scored in a breakout 2017-18 at Fiorentina.
That form proved good enough to earn international honours, but the last of his five caps also came in 2018. At 25, he still has plenty of time to get back on track.
Record man Ronaldo falls flat
Ronaldo has 31 league goals and is two shy of chalking up the most prolific Serie A season in Juventus history, even if Lazio's 35-goal Immobile is now surely out of reach. But he was brought to Turin to help bring Champions League glory.
The sight of that wider goal appeared to be lost by all concerned as Sarri indulged a spiralling shot count (10 - two on target, seven blocked) and another 90 minutes in the legs for the 35-year-old.
Juventus wrap up their Serie A season at home to Roma on Sunday (AEST), when Cagliari are on the road at in-form Milan.