Allegri had dropped Gianluca Frabotta, Nicolò Fagioli and Alessandro Di Pardo as punishment for turning up late to a training session, while Luca Pellegrini and Paulo Dybala were injured.
Koni De Winter struck first for Juve, before Weston McKennie doubled Juve's lead.
Then in the second-half, Matias Soulé capped off an impressive display with a goal, aided by a big deflection.
McKennie, meanwhile, was spotted on the bench with strapping around his knee.
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