Interesting game.
Allegri made a good call in playing what was almost 4-3-3 in the first half. That makes Conte, having chosen to play 3-5-2, to either lose width on one or boths sides of the pitch or leave the defence to play three on three. He chose to play three on three and so Juve were continually at full stretch.
The goal was just an individual error, but the systems caused Juve to be pinned back in their own half and allowed Milan to contol the game, with Juve being fortunate to only be one goal down at half time.
Conte then goes to 4-3-3, which allows Juve to up the tempo, force Milan back and create a two v one situations on the flanks on both sides, which was what caused the goal. Milan went back to their more orthodox 4-3-1-2 system, but I don't understand them not marking Pirlo with Emanuelson once they go to that shape.
I thought Milan surrendered territory too readily and ought to have changed to 4-4-1-1 when Ambrosini came on, which would have allowed them to close the space on the flanks better than they could with 4-3-1-2.
Good result for Juve, but very lucky.