It may only have been a friendly between the Italian arch rivals, but tempers threatened to boil over at times, especially in a feisty second half in stifling Nanjing.
The game ended 1-1 after 90 minutes, with Cristiano Ronaldo drawing Juventus level with a deflected second-half free-kick following De Ligt's own goal.
Then the 41-year-old Buffon -- more than twice De Ligt's age -- sprang to the fore in the shootout, making a triumphant return to the Serie A champions after a year with Paris Saint-Germain.
New Juventus coach Maurizio Sarri said he could "accept mistakes" -- for now.
"The feeling is that we can improve a lot, especially in the offensive part of the game," said the former Chelsea boss.
"It is about changing the way of thinking and it is not easy to happen in a short time."
Dutch teenager De Ligt, who joined Juventus last week from Ajax for a reported 75 million euros ($85 million), came on as a substitute during Sunday's 3-2 defeat to Tottenham Hotspur in Singapore.
Sarri started the 19-year-old in the "Derby d'Italia" but the central defender got off to the worst possible beginning, directing the ball past goalkeeper Wojciech Szczesny with his knee to give Inter the lead.
De Ligt, who was one of the most coveted players in world football before his big-money move, was largely untroubled thereafter before being substituted at the break.
It was only a pre-season friendly as part of the International Champions Cup, but Antonio Conte's Inter dealt out some rough treatment to Ronaldo.
Three times in the first half, in a match played in sweltering conditions in eastern China, the Portuguese forward was sent sprawling to the turf.
There was a flashpoint in the 51st minute when Juventus substitute Merih Demiral -- who was to score the winning penalty -- lashed out while waiting for his side to take a corner.
Minutes later skipper Leonardo Bonucci talked himself into a yellow card as the referee struggled to keep control.