The Hammers attracted close to 54,000 fans to their official opening of the London Stadium in their eventual 3-2 defeat to the Italian champions.
A brace from Andy Carroll after goals from Paulo Dybala and Mario Mandzukic inside 21 minutes got the East Londoners back in touch prior to Simone Zaza's late winner in what was a decent hit-out a week before the new Premier League season.
Of the match, Bilic told West Ham's official website: "It was a good test for us.
"We started sloppily – we hit the post after 15 minutes but they are a top class team and if you are on the back foot and give them a yard, they can pass the ball and play football.
"If you give them three or four yards then it's too easy for them. That's what we gave them at the start – okay we played three nights ago and were a little bit tired – but then after that we came back into the game and changed the rhythm.
"It was much more aggressive, we made it harder for them and Andy scored his type of goals. They are of course very important for us and he is great for us.
"Then we put some young players in because we don't want to risk injuries and that kind of things. We thought it was going to end 2-2, but then we conceded one that from our point of view was too easy and sloppy.
"It was a packed Stadium against one of the biggest clubs and best teams in Europe.
"It was a good test for us and great to see the fans filling our Stadium again."
West Ham commence the 2016/17 league campaign with a short trip to Stamford Bridge to take on Chelsea on Monday, August 15.