The Brazilian struck on debut in the 3-0 win, with James Olayinka and Bukayo Saka also struck.
Emery said, "It's our first match, we are working very well here in Los Angeles and the first match was good to use different young players, to give them chances to show their quality, commitment to work and to be with the idea to help the team.
"It was the best for us today. Some moments were for the young players, this was one of those moments. The atmosphere here was perfect, a lot of Arsenal supporters and we had a good day here."
On Martinelli, Emery continued: "Our idea is to give every young player chances to be with us, first in the training ground and after playing matches like today. The idea is to give them more chances in other matches. They will win the possibility to be with us with their performances."