It was Udinese's first victory of the season in all competitions.
"First of all, I compliment Milan for an excellent opening 10 minutes in which they really pinned us back," said Guidolin.
"Max had said he wouldn't change his system, but I didn't believe him and indeed I was right, as he fielded two wide attackers with a centre-forward.
"When we moved to four at the back, with a diamond in midfield, we managed to close down the spaces better and create more chances.
"In any case, Max has everything needed to revive this Milan side."