Cristiano Ronaldo became the first player to score 400 goals in Europe's top five leagues but couldn't stop Juve from dropping their first points of the season following a 1-1 Serie A draw with Genoa on Saturday.
The Croatian boss replaced Davide Ballardini before the worldwide break for his third spell in charge of Genoa and he made an immediate impact as the Italian champions failed to record a victory for the first time in nine league games this season.
He tapped in after Joao Cancelo's shot was blocked - having earlier hit the post with a header.
Lionel Messi is next best on 389.
Leonardo Bonucci could easily have been in the home dressing room at Old Trafford as he prepares for Tuesday's momentous Champions League tie.
Energised, the 23-year-old should have levelled seconds later, outjumping Leonardo Bonucci but his header went wide.
Chong scored twice in United's 3-0 win against Sunderland's U23s on Friday and has been rewarded with a call-up to first team training.
Juve are now four points clear on top of the table ahead of second-placed Napoli.
Juventus paid heavily for failing to restrain Genoa when Daniel Bessa headed a cross from Christian Kouame into the back of the net at 67 minutes.
The Curacao-born 18-year-old is considered, alongside Angel Gomes, to be United's most exciting academy product and he impressed on the club's tour to the United States last summer.
SPAL took the lead from the penalty spot after 38 minutes. Every match has to be won on the pitch in 90 minutes.