Joe Allen scored after 17 minutes as he tucked home a rebound and Suso sealed the win late on in the International Champions Cup on Saturday in Charlotte.
Brendan Rodgers's side will now face Manchester United in the tournament final in Miami on Monday night.
Striker Daniel Sturridge missed the game as he returned to the UK for treatment on a minor hamstring injury.
Rodgers said he expected Sturridge to be fit to face Borussia Dortmund in a friendly on 10 August.
Liverpool, who were second in the Premier League last season, begin their 2014-15 campaign at home to Southampton a week later.
The Reds lost to Roma on their US tour before beating Olympiakos and Manchester City.
Liverpool: Mignolet, Kelly, Toure, Coates, Robinson, Lucas, Henderson, Allen, Lambert, Ibe, Sterling.
Substitutes: Jones, Johnson, Enrique, Gerrard, Coutinho, Sakho, Can, Suso, Coady, Skrtel, Peterson.
AC Milan: Abbiati, Abate, Rami, Bonera, De Sciglio, Muntari, Essien, Saponara, Niang, Pazzini, El Shaarawy.
Subs: Agazzi, Honda, Poli, Zapata, Constant, Cristante, Gabriel, Zaccardo, Mexes, Mastour, Albertazzi, Pinato, Balotelli, Modic. Coach: Inzaghi.