The Hammers were beaten 3-1 by City, losing to an Erling Haaland hat trick.
While Alvarez admits the result did sting, he was delighted to be back in action after a lengthy absence with a hamstring injury.
"Of course I am very happy to play my first game this season as a starter in the Premier League," he told club media.
"It has been a long journey (since the injury in the Copa América) and a lot of hard work, but I always told myself that everything happens for a reason and in that moment maybe you don’t understand but this is what makes you stronger.
"As a player you want to go onto the pitch as soon as possible but of course the medical staff need to control you! It’s difficult sometimes but you need to follow the way and I think we did the right things
"It was a good challenge for me today because I can prove my hamstring (is recovered). It’s always so good to play against these kind of teams, because in my opinion City is one of the best teams in the world.
"They challenge you to see where you are and where you can improve and of course we are sad (at the result) but we need to look forward because we have a very strong team and in my opinion we can do very good things."