Rebic came off the bench at half-time to bag a brace around the Theo Hernandez volley.
Pioli enthused, “We were a little tense at the start and Udinese had scored early on, allowing them to make the most of their characteristics. I introduced a player like Rebic, who I thought could provide a change of pace, and he deserves credit for his impact.
“I have 19 first choice players, it's up to them to be ready when called upon, it is not the job of the coach to regenerate his players. We've got to continue like this, as January will be very important for our future."
Theo Hernandez remains Milan's top scorer with five Serie A goals, despite being a left-back.
“I was fortunate enough to play with Antonio Cabrini, so I know a good full-back when I see one," smiled Pioli.
“I push Theo on every day in training, because I believe he can become one of the best in the world. If he continues like this, he's bound to be spotted by his national coach too."