An own goal by Louis Poznanski had given the Gunners a second half lead that was cancelled out by Robert Lewandowski.
20-year-old Eddie Nketiah stepped up to score the winner with two minutes remaining.
Joe Willock looked comfortable in the starting line-up while Tyreece John-Jules and Bukayo Saka didn't look out of place after coming on as late substitutes.
With Arsenal stuttering in the transfer market this summer, Emery was encouraged by the performance of his young players.
“We have the responsibility with the young players to give them chances," said the Spaniard.
“Some players will be with us in the season, each minute they show their performance against big players. For example the one-to-one Nketiah against Sule [was encouraging].
“Will I rely more on them? It depends on their performance. Against Colorado Rapids a lot of young players played. We need them for the moment but also in the future.
“Our responsibility in this club for the history, present and future is to give young players chance. If they deserve minutes they'll get minutes. I'm very happy with them."