Paul Pogba and Mario Mandzukic were both on target as Juventus won 2-1 against Lechia Gdansk.
Juve were in front after only four minutes when Paulo Dybala's corner was headed home by Pogba.
But Massimiliano Allegri's men suffered a blow shortly afterwards when Giorgio Chiellini was forced off injured. The Serie A champions have already lost fellow defender Andrea Barzagli to a three-week layoff.
Sami Khedira, signed from Real Madrid earlier in the summer, came off the bench on the hour for his first appearance for his new club.
Adam Buksa brought Lechia back on level terms in the 82nd minute, but the visitors were not to be denied when Mandzukic netted his first Juve goal when he converted a Roman Macek cross.
Napoli enjoyed a more emphatic victory, winning 5-1 against Cittadella at their Dimaro training camp.
Raul Albiol put Maurizio Sarri's side in front, but was then forced off after a clash of heads. Lorenzo Insigne scored twice, and after Claudio Coralli pulled a goal back efforts from Omar El Kaddouri and Dries Mertens put the gloss on the scoreline.
Lazio's preparations for the Italian Super Cup clash with Juventus in Shanghai on Aug. 8, as well as the first leg of their Champions League playoff in three weeks' time, suffered another setback as they slumped to a 3-0 loss at Mainz.
It was their fourth consecutive loss in preseason as Yunus Malli, Jairo Samperio and Christian Clemens fired the Bundesliga outfit to victory.
Villarreal played out a 1-1 draw with Derby County. The Spanish side were in front just before the half hour through Leo Baptistao, but the Rams found a second-half equaliser courtesy of Andreas Weimann.
Sunderland suffered defeat in their preparations for the new Premier League season, with goals from Cedric Evina and Harry Forrester giving League One Doncaster Rovers a 2-0 victory.
North-East rivals Newcastle United also came unstuck, losing 2-1 at York City. The League Two side raced in front in the first half, the goals coming from Anthony Straker and an unnamed trialist. Ayoze Perez got on the scoresheet for the Magpies in the 75th minute.
There was better news for Leicester City under new boss Claudio Ranieri, as they won 2-1 at Championship side Rotherham United. Riyad Mahrez and David Nugent put the Foxes in control before a late consolation from Grant Ward.
Bayer Leverkusen warmed up for their DFB-Pokal opener at Sportfreunde Lotte in 10 days' time with a 4-0 thumping of Levante. Stefan Kiessling, Hakan Calhanoglu, Karim Bellarabi and Sebastian Boenisch found the back of the net, while Juanfran Garcia saw red in the first half for the Spanish side.