Spurs were beaten 2-1 by the MLS select in Denver but the result was brushed to the side when taking into account the learning curve for some of the clubs less experienced players.
Homegrown 18-year-old Onomah was lively for Tottenham during the second half at Dick's Sporting Goods Park and admits it was an important game to be a part of from an educational point of view.
"With the likes of Kaka and David Villa playing, it was a great experience," he told the club's official website.
"I grew up watching those players and to see them in action against us was amazing.
"Obviously when I came on we were losing 2-1 so my first thought was that I needed to come on and make an impact.
"I had two chances, the first one I should have hit harder, but the keeper saved them both, so I learned lessons from those incidents and I'm determined to do better next time.
"All in all, we created chances together as a team and there were definitely a lot of positives to take from the game."